Season 21 superfinal games 41-50

After 50 games Stockfish leads 7-4 with 39 draws. Stockfish extended its lead to 3 after two game pair wins and only one game pair win for Leela. The gap can still be closed by Leela, this is only the halfway point of the superfinal. It appears though that Stockfish has better chances of winning.

In game 41 both engines castled long, there were many early exchanges and long PV agreements. On move 23 only QRN vs QRB remained with low evals. The game reached a N vs B ending, Leela was a pawn up but it was only good for a draw.

In game 42 Stockfish castled long and Leela chose to keep its king uncastled. Stockfish pushed pawns on the king side, then exchanged queens and went a pawn up. Stockfish's eval remained around 1, after some shuffling it moved its rooks to the king side. Leela finally castled short on move 31, it stopped to think for 19 minutes when Stockfish exchanged pawns and opened the king side. Leela's eval jumped a little but was still under 1.

Stockfish's eval increased a little, Leela traded pawns on the queen side, perhaps to create counter threats on the white king. On move 40 Leela moved without thinking as it often does, Stockfish thought this was a blunder and its eval jumped close to 4. It pushed the g pawn, Leela realized it couldn't take the pawn and its eval jumped over 2. Stockfish now had a passer facing the black king, with a back rank mate threat. Leela quickly exchanged pieces and reduced to a R vs BB ending.

Leela captured the g pawn, Stockfish did not blunder the 7-man ending though there were several moves with only one winning choice. It managed to push the b pawn forward, finally promoting to a queen on move 69. The game ended shortly afterwards. Stockfish wins the game pair, it leads 6-3.

In game 43 the engines castled in opposite directions, the white king had little pawn support while the black king was weak on dark squares. After exchanging the DS bishops Leela pushed a pawn to h6. Stockfish became more uncomfortable and its eval went over 1.5, Leela's eval was around 1 when the game reached a QRN vs QRB position on move 36.

The engines played out long PV agreements, Stockfish's eval kept increasing. Stockfish captured the white h pawn while Leela captured the black a pawn and created a passer on the queen side. Stockfish tried to use its pawn majority on the king side without success, Leela's confidence grew and its eval increased. On move 55 the engines exchanged queens and evals were over 4.

Leela pushed pawns on the queen side and the white king came forward to support. Stockfish gave a pawn to clear a path for the f pawn, Leela used its knight to block the black pawns. After exchanging rooks Stockfish could not stop the advancing white pawns, Leela queened a pawn and the game ended in a tablebase win.

In game 44 Stockfish castled short and the DS bishops stayed on the board longer. Eventually Leela also castled short, Stockfish created a passer on the queen side, its eval stayed around 1. On move 31 the game reached a QRR vs QRR position and Stockfish went a pawn up. It couldn't push the passer forward and the engines mostly shuffled while evals came down. On move 59 Leela regained the pawns and exchanged queens. Stockfish went a pawn up again but the double rook ending was a draw and the game was adjudicated. Leela wins the game pair, Stockfish leads 6-4.

Games 45-46 started with a 24-ply book in the English symmetrical, hedgehog variation. There was only one pawn exchange and all pieces were on the board. In game 45 the engines opened the queen side, then exchanged minor pieces and a pair of rooks. Leela had a doubled passer on the queen side but it couldn't push it forward. The engines shuffled and evals came down, the game was adjudicated when the pawns stopped moving on move 74.

In game 46 there were no exchanges and the queen side stayed closed. On move 25 the pawns stopped moving and the engines started to shuffle. On move 66 Stockfish exchanged knights and then continued the shuffle. Evals increased a little, Stockfish's eval was over 2 when on move 95 it finally pushed a pawn on the king side. The king side opened and most of the black pieces were too far to help the black king. Evals increased quickly as the black king ran from the attacking white pieces.

Leela tried to block the center to protect its king. Stockfish sacrificed a rook and its queen broke through the center, for a few moves Leela's eval dropped. It was false hope, the black king was in a net and Leela had to give material to avoid mate. The game reached a QB vs RBB position on move 120.

There were too many targets for Stockfish as well as an exposed black king. Stockfish captured two pawns, then captured a bishop. The white passers moved forward and mate followed. Stockfish wins the game pair, it leads 7-4.

In game 47 the center was blocked, Leela pushed the h pawn and exchanged it, letting the rook out. Both engines castled long and the queens were exchanged. Evals came down as the white king walked to the king side and Leela opened the queen side. A series of exchanges reduced to a RB vs RN position and Leela went a pawn up. Leela had a passer in the center but Stockfish kept the white king away, evals were low enough for adjudication. In game 48 the king side remained closed, Leela moved its king there without castling. After a few minor piece exchanges Stockfish castled long, then the engines started to shuffle. Stockfish's eval stayed around 1, one pawn exchange and a few pawn moves kept the shuffle going until move 121. Evals came down after the engines opened the king side and started exchanging pieces. The game reached a RN vs RN position and was adjudicated on move 142.

Both engines thought the book opening of games 49-50 was a draw with evals close to 0. The games repeated the first 12 plys, opening the center with white a pawn up. In game 49 Stockfish castled long and gave a second pawn, Leela was behind in developing the king side. By the time Leela's king side pieces moved and it castled its king Stockfish regained the two pawns and queens were off. Evals were around 0 and the engines continued to exchange pieces, the game reached a tablebase draw on move 51. In game 50 both engines kept their kings in the center without castling. Stockfish was a pawn up but evals stayed around 0. The engines gradually exchanged pieces until only RB vs RB remained on move 38, the game reached a tablebase draw again.

Season 21 superfinal games 31-40

After 40 games Stockfish leads 5-3 with 32 draws. There were 4 game pairs that ended in double draws, though it is possible Stockfish missed a win in game 34. Then Stockfish won a game pair win, ending a streak of 14 draws.

Games 31-32 started with a 6-ply book in the Scandinavian defense, with the black queen moving forward early. In game 31 Leela pushed the black pieces back. After Stockfish castled Leela gave a pawn on the king side and then castled long. Leela captured a rook for a knight, Stockfish pushed pawns on the queen side and evals came down. The white king hid behind a black pawn, in a series of exchanges the engines reduced to a QR vs QB position. After exchanging queens the pawns raced forward on both sides, but neither engines could force a promotion and the game was adjudicated. In game 32 both engines castled short, there only a few exchanges after the start. Evals came down as the engines played out a long PV agreement, the game reached a queen ending with white a pawn up. Evals were close to 0, Stockfish started to give checks and the game was adjudicated.

In game 33 the engines opened the center, Leela went up a pawn and created a doubled passer on the queen side. Both engines focused on the queen side, evals came down slowly as pieces were exchanged and on move 32 only QRB vs QRB remained. There were a few pawn trades on the king side, then queens were exchanged and the game was adjudicated.  In game 34 early exchanges forced the black king to move uncastled. The engines played out a long PV agreement in which Stockfish traded RBN for Q. On move 27 Stockfish's eval jumped over 2.5, the engines reduced to a Q vs RBN position with white 3 pawns up. Leela thought long, about 30 minutes for 4 moves, its eval also increased to around 1. At one point Stockfish's eval was more than 3.5:

However, Stockfish couldn't find a way to break through. Leela blocked the white passers on the queen side with pieces, and built a fortress that the white queen could not penetrate on its own. On move 96 Stockfish traded pawns on the king side, the white king was still blocked and couldn't move forward. Evals slowly came down, pawn moves extended the game until it was finally adjudicated on move 190. Did Stockfish miss an opportunity or was it a mis-evaluation?

In game 35 the center was blocked, Stockfish castled long and Leela kept its king in the center, with evals under 1. Leela gave a pawn on the queen side, opening files for it to threaten the black king. Stockfish kept its king safe and Leela shifted most pieces to the king side. Leela regained the pawn, evals came down enough for the draw rule, despite many pieces on the board. In game 36 the engines opened the center and kept their kings uncastled after the start. In a long PV agreement Stockfish castled long, the engines exchanged pieces until only RRN vs RRB remained on move 25, evals under 0.5. On move 34 Stockfish's eval jumped over 1, but it dropped right back down, not sure what Stockfish saw. The engines continued to exchange pieces until reaching a rook ending, white was a pawn up but it was still a draw.

Games 37-38 started with black a pawn up in the Queen's Gambit Accepted opening. In game 37 Leela regained the pawn and there were no exchanges for a while after the start. The engines opened a file on the queen side and then opened the center, evals came down. All pieces were on the board until move 28, Leela went a pawn up and then the engines reduced to a RB vs RB position. The game was adjudicated when evals were low enough. Game 38 started similarly, this time the center remained closed and the first piece exchange was earlier. The engines exchanged queens and evals came down, the exchanges continued until the game reached a rook ending on move 44. The game ended in a tablebase draw.

Games 39-40 started with a 7-ply book in the Old Indian, Wade variation. In game 39 there were very few exchanges after the start, Stockfish's eval stayed around 1.5. On move 19 the exchanges began, at first opening the center files. Leela's eval increased to around 1, it went a pawn up and then the engines reduced to a RB vs RN position on move 35. Leela didn't seem to have a plan and the engines shuffled for a long while. On move 87 Leela exchanged pawns on the queen side, Stockfish's eval came down quickly to 0. The shuffling continued until Leela lowered its eval, the draw rule stopped the game on move 154. 

In game 40 Stockfish pushed pawns on the king side, it gave a pawn and weakened the black pawn structure. Leela castled long while Stockfish kept its king uncastled, the engines played out long PV agreements and Stockfish's eval increased to around 2. A series of exchanges started on move 18, Stockfish regained the pawn and created a passer on the king side. Leela's eval increased over 1 as Stockfish pushed the passer to the 6th rank.

The black bishop was trapped in the corner, it blocked the white passer and was protected by a rook. Stockfish slowly moved its king to the king side to avoid any surprise attack, then it exchanged bishops on move 43. 

Leela could not prevent the pawn promotion and it lost its rook. The black queen moved forward to threaten the white king, Leela also created a passer and pushed it forward. This only delayed the inevitable, Stockfish made sure its king was safe, it gained material and finally mated. Stockfish wins the game pair, it leads 5-3.

Season 21 superfinal games 21-30

After 30 games Stockfish leads 4-3 with 23 draws. There was one game pair with two white wins, the book start bias was probably a factor, but the two wins were not similar. Leela won a game pair to reduce the lead to just one point. 

TCEC was hit by a typhoon during game 29, at least the TCEC hardware in Shanghai was. As a result there was a power outtage and the game had to be resumed after a break. There were still problems that forced a manual adjudication in a clear draw. The tournament was halted for a day to wait for the storm to pass. 

I should also note that the Olympic games in Tokyo have started, causing some distraction for me and my TCEC posts.

In game 21 there were no exchanges after the start, the engines developed behind the pawn lines. On move 18 a pair of pawns was exchanged and the a file was opened, Stockfish doubled its rooks in the open file. There was one more pawn exchange in the center and evals came down. Leela offered another pawn but Stockfish just shuffled, the draw rule ended the game with all pieces on the board. In game 22 Stockfish castled long, Leela opened the b file and Stockfish tried to open the king side with its pawns. Stockfish offered a rook for a knight but Leela preferred to use its knight to block the h file. After a few piece exchanges the engines started to repeat and shuffle and the game was adjudicated.

In game 23 Stockfish's eval started around 1 and it slowly drifted down, there were no exchanges after the start, Leela castled long and Stockfish kept its king in the center. The engines exchanged minor pieces but all pawns were on the board until move 29. Evals stated to drift up, the engines opened the king side, then Leela gave two pawns and opened the queen side. The black king scrambled for safety on the king side, Leela captured the pawns back and created a central passer. After exchanging queens Leela went a pawn up. 

The engines played out a long PV agreement, there were no exchanges but evals kept increasing. Stockfish doubled rooks on the queen side but its attack on the white king was weak. Leela traded pawns on the king side and then all rooks were exchanged, leaving a BN vs NN position on move 64.

After trading pawns Leela created connected passers in the center, and with the king supporting them Stockfish could not stop their advance. Leela started to gain material and mated eventually.

The start of game 24 was similar to the previous game, with no exchanges and evals mostly stable. On move 17 the engines started a series of exchanges that opened the king side, and Stockfish went a pawn up. On move 28 Leela moved without thinking and Stockfish's eval immediately jumped over 2.5.

Leela saw right away that it blundered, after thinking for more than 10 minutes. The e3 knight was unprotected, Leela tried to save it for a few moves. In a series of exchanges the black knight was traded for a bishop, but Stockifsh captured a second pawn in the process. Leela moved its queen forward in a QBN vs QBN position, it avoided exchanges as long as it could but on move 52 Stockfish traded a bishop for a knight, its eval over 11.

Leela's defense crumbled, Stockfish exchanged pawns until all the black pawns were gone and there were two connected white passers in the center. Leela gave its queen to avoid a white queening, mate followed. There were two white wins in this opening, though the games were very different. Stockish leads 4-2.

In game 25 evals were below 1 after the start, the engines exchanged a pair of knights and opened a file on the queen side. Stockfish was a pawn up with a central passer, it offered a rook for a bishop but Leela wouldn't take since this would connect a second black passer. Stockfish's eval went over 1 first, then Leela's eval followed as the engines played a long PV agreement. In a series of exchanges the engines reduced to a RRB vs RBN position, with black 3 pawns up.

Evals continued to increase slowly. Stockfish gave a pawn and created a passer on the king side, then pushed it to the 2nd rank. Leela exchanged a pair of rooks, and watched the black passers carefully. It took Leela a while but eventualy it captured both black passers.

The white king moved forward, Stockfish didn't have the strength to protect all its pieces and pawns. Leela captured the black a pawn to create a passer, Stockfish was forced to lose a piece to stop it, game over.

Game 26 repeated the start of the previous game for 13 plys, Leela was a pawn up with a central passer, and an open file on the queen side. This time the engines exchanged queens and a pair of rooks through the open file, evals started to come down. The engines gradually exchanged pieces and pawns, only RBN vs RBN remained on move 35. Stockfish captured the black passer and went a pawn up, but evals were close to 0 and the game was adjudicated when the pawns stopped moving. Leela wins the game pair, Stockfish still leads 4-3.

In game 27 Leela pushed pawns on the king side and opened a file to expose the black king, then it castled long. After exchanging queens and a pair of rooks Leela was a pawn up, both kings moved to the center as most pieces were gone. The engines continued to exchange pieces until reaching a RNN vs RBN position, Stockfish created connected passers on the king side. Leela cleared the black pawns on the queen side while Stockfish pushed a passer to the 2nd rank. Leela lost a knight for the passer but was 3 pawns up. Evals came down slowly, Leela captured the remaining black pawn but didn't push its passers and shuffled instead. When Leela finally pushed its pawns forward Stockfish gave its bishop and captured 2 pawns. Leela was 2 pawns up in a RN vs RN position but both engines agreed the position was a draw and the game was adjudicated. In game 28 Stockfish pushed pawns on the king side, then didn't castle but moved its king to the king side despite having no pawn support. The engines exchanged a few pawns and pieces and opened files, evals came down close to 0. Both engines seemed ready for a draw, after exchanging all rooks the game was adjudicated.

Games 29-30 started with a short 6-ply book in the French Tarrasch variation. In game 29 the engines developed pieces behind their pawn lines, Stockfish pushed pawns on the queen side and Leela's king walked to the king side. Evals came down quickly, low enough for the draw rule on move 21. Leela opened the king side and attacked, Stockfish countered with a rook sacrifice and forced a perpetual check draw. Game 30 started similarly, this time Stockfish castled its king. Leela opened the queen side and gave a pawn to create a passer on the 2nd rank. Stockfish gave a rook for a bishop to capture the passer, the after a series of exchanges the game reached a rook ending with white a pawn up. Evals werew close to 0, the game was adjudicated once the pawns stopped moving.

Season 21 superfinal games 11-20

After 20 games Stockfish leads 3-1 with 16 draws. No change in the score after 10 straight draws.

In game 11 Leela castled long, Stockfish moved its king and castled short by walking. There were many early exchanges that opened the position and only QRN vs QRN remained on move 25. Evals were low and the engines only shuffled, the game was adjudicated by the draw rule. Game 12 started similarly, though there were less exchanges. Stockfish opened the king side and tried to attack the black king. Leela exchanged pieces and only RRN vs RRN were left on move 32, the black king was exposed but not in danger. Stockfish exchanged a pair of rooks and went a pawn up, after the pawns stopped moving the engines started to shuffle. A few exchanges led to a RN vs R ending with black a pawn up, the game was finally adjudicated on move 147.

In game 13 there were a few early exchanges and the engines opened a file in the center. Evals came down close to 0, the engines exchanged all rooks and the game reached a QB vs QN position on move 27. The game was adjudicated in a queen ending with both queens giving check in turn. In game 14 there were less exchanges, Stockfish pushed pawns in the center and managed to get a passer to d6. Leela blocked the passer and evals came down, a series of exchanges reduced to a RRB vs RRB position. Leela captured the passer and the game reached a drawn rook ending.

In game 15 Leela castled long, a series of exchanges opened the center. Evals came down as the engines exchanged pieces and Stockfish castled short. Leela opened the king side, the black king hid behind a white pawn and evals were close to 0. The engines continued to exchange and move pawns, the game ended in a tablebase draw. Game 16 started similarly, this time queens were exchanged early as well and both engines castled long. Evals came down and the exchanges continued, the game reached a RB vs RB position on move 33. Stockfish was a pawn up and it wouldn't lower its eval, the engines shuffled and the game was finally adjudicated on move 88.

Games 17-18 started in the St. George defense with white a pawn up and with a passer on the queen side. In game 17 Stockfish's eval was around 1 from the start. On move 8 the engines started to play out long PV agreements until move 20, queens were exchanged, Stockfish castled while Leela kept its king in the center. Evals came down, Leela's passer did not advance, pawn moves and exchanges kept the game going. The game was adjudicated in a RN vs RN position. In game 18 Stockfish gave back the pawn, both engines castled short and Stockfish pushed the passer forward. Stockfish's eval stayed around 1 while the engines mostly shuffled, the white passer reached the 6th rank but couldn't advance further. Leela went a pawn up, Stockfish's eval drifted down in a long shuffle, on move 85 the exchanges began. The engines reduced to a RRN vs RRB position, the white passer advanced to a7 where it was blocked. The game was adjudicated once the exchanges stopped.

In game 19 the black king was forced to move without castling. Leela attacked with a queen and knight and captured a rook for a bishop, however evals were low. The engines exchanged pieces and on move 28 only QR vs QN remained with black two pawns up. Stockfish had connected passers on the king side that Leela had to watch, for a while there was no progress and then the exchanges began. The game was adjudicated in a drawn R vs N position. In game 20 there were long PV agreements after the start. In the first PV agreement the engines opened the king side, and in the second both engines castled long while evals came down. After a series of exchanges only QNN vs QNN remained on move 29. Stockfish moved its pieces forward to attack, while Leela created an advanced passer in the center. The engines reduced to a knight ending, Stockfish captured the passer and was a pawn up but it was not enough. The pawns stopped moving and the game was adjudicated.

Season 21 superfinal games 1-10

After 10 games Stockfish leads 3-1 with 6 draws. The score was 1-1 after the first two game pairs, then Stockfish won two more game pairs and it has a small lead. In game 10 Leela made a long term blunder in what appeared to be a drawn position, playing without thinking. 

Openings for the superfinal were prepared by Jeroen Noomen and GM Matthew Sadler, see the details here. GM Sadler is also commentating many of the games live on his Silicon Road stream.

Games 1-2 started with a 22-ply book in the Sicilian Richter-Rauzer, Neo-modern variation, with white castling long and the black king in the center uncastled. In game 1 Stockfish opened the queen side and threatened the white king. Leela played a few moves in a PV agreement without thinking, Stockfish's eval came down. Leela opened the king side, Stockfish gave a rook for a bishop, its king was stuck in the center but safe enough. The engines started to exchange pieces, eventually reaching a drawn queen endgame. 

In game 2 Leela did not open the queen side immediately, Stockfish had more time to strengthen the defense of its king and its eval went over 2 quickly. Leela's eval went over 1.5 after Stockfish opened a file on the king side, the black king was stuck in the center. The engines exchanged queens and were down to 3 pawns each. Leela thought for 30 minutes before moving its king to the king side, trying to build a fortress around it with its pieces.

The engines seemed to be shuffling for a while, Stockfish's eval increased while Leela's eval was more static. The white bishops controlled a lot of space, the black king side rook was trapped and the black pieces became increasingly passive. On moves 35-36 Stockfish moved its king, apparently without purpose, and suddeny Leela's' eval jumped over 3. Stockfish doubled rooks on the e file and went a pawn up.

Stockfish threatened mate on the back rank. The engines exchanged pieces until reaching a rook ending. Stockfish was a pawn up and the black king was isolated on the king side, Stockfish promoted the c pawn to a queen and won. Stockfish wins the game pair, it leads 1-0.

There were no exchanges after the start of game 3, Stockfish's eval started over 1. Stockfish opened the h file and exposed the white king, though its own king was also at risk. Stockfish attacked with a queen and knight, the white king seemed to be in danger but Leela defended well and evals continued to increase. After exchanging queens and a pair of bishops the black attack was over, Leela grabbed a pawn on the queen side and created doubled passers.

Leela captured a second pawn, after exchanging a pair of rooks only RBN vs RNN remained. Stockfish managed to create a passer and to capture one of the white passers. Leela was still a pawn up and its eval slowly increased. 

Both engines used a knight to make sure the passers can't move forward. After exchanging rooks Leela gradually captured black pawns, including the c passer. It was 3 pawns up and Stockfish could not stop all the advancing white pawns. Leela promoted to a queen and won.

In game 4 Stockfish's eval was over 1 from the start. There were no exchanges and the engines played behind their pawn lines. On move 26 the engines locked the king side and started to shuffle. Leela's eval dropped to 0, Stockfish did not find a way to break the pawn wall. A few pawn moves and piece exchanges extended the game, Stockfish gave up and lowered its eval for adjudication on move 115. Leela wins the game pair, score is now 1-1.

Games 5-6 started with a 26-ply book in the Semi-Slav defense, Meran, Wade variation. Only one pair of pawns was exchanged, white had a central passer, the black king was uncastled in the center. In game 5 the engines played out a long PV agreement, Stockfish gave a rook for a bishop and pawn and castled on move 26, its eval slowly coming down. After the pawn structure stabilized the engines started to shuffle, evals came down and the game was adjudicated early. In game 6 the white passer reached the 7th rank before Leela captured it. The engines again played out a long PV agreement, this time the black king moved and did not castle, Stockfish's eval stayed around 1. The engines started to exchange pieces and evals came down. The game reached a rook ending, white was a pawn up but the position was a draw.

Games 7-8 started in the Czech Benoni defense, in both games Stockfish's eval went over 1.5 after book. The engines exchanged DS bishops early, the black king side rook moved and white castled long. In game 7 Stockfish gave a pawn and opened the queen side. Leela pushed pawns on the king side while Stockfish increased the pressure on the white king. After exchanging queens only rooks and knights remained on move 23, evals were under 1. A series of exchanges reduced to a RN vs RN position, Leela was a pawn up but it could only shuffle. After 30 moves Stockfish gave the knight for two pawns, Leela's eval came down and the game was adjudicated. 

In game 8 Leela kept the queen side closed, and the engines started to shuffle early. Stockfish's eval was over 1.5 but evals didn't change for a long time. There was one pawn exchange on the king side, and the engines reduced to rooks and knights as in the previous game. It appeared that Stockfish had no plan of attack or improvement. Then on move 40 Leela moved a pawn on the queen side and Stockfish's eval immediately jumped over 2. After doubling rooks on the f file Stockfish pushed a pawn forward and opened the file, its eval over 3.5. Its eval continued to increase after the engines exchanged a pair of rooks.

Stockfish gave the e pawn so that its d pawn became a passer. It moved its two knights forward while the black pieces were passive as Leela tried to block the white rook. Stockfish was very patient, it was hard to see progress but evals increased steadily. Stockfish regained the pawn and finally managed to exchange rooks on move 85, then it went a pawn up.

The double knight ending was slow. Stockfish captured a second pawn, then Leela gave a knight to stop the white d pawn. The win was a matter of time. Stockfish wins the game pair, it leads 2-1.

Games 9-10 started with a 20-ply book in the Sicililan Najdorf, Adams attack. The engines castled in opposite directions and all pieces were on the board, with one pawn exchange. In game 9 Leela pushed pawns on the king side and Stockfish pushed pawns on the queen side. A black pawn reached a3 and a white pawn reached h6. Both kings were weak on the dark squares and both were threatened by major pieces on open files. Stockfish lost its DS bishop in a trade, Leela used its DS bishop for defense. The position became stable on move 26, Leela's eval slowly came down until the game was adjudicated on move 66.

The start of game 10 was similar, though both engines stopped their advancing pawns earlier. The DS bishops were exchanged and so were the queens, the kings were not threatened. Evals slowly drifted down as the engines exchanged pieces, on move 34 only RN vs RN remained and evals went under 0.5. On move 37 Leela moved without thinking, as it sometimes does. Stockfish's eval immediately jumped over 3, blunder ?!

Leela spent more than 40 minutes on its next two moves, and its eval jumped as well, over 7 after move 40. The advantage was not evidently clear, more subtle and long term, but both engines had no doubt it was there. Leela did not try to defend its a pawn, both engines were more concerned about the king side. After exchanging knights Stockfish captured the f pawn and Leela captured the white a pawn. Both engines pushed passers on the queen side and both were a square away from promotion.

Leela's rook was on front of its passer, the white king was strong enough to capture the passer on its own. As the white king walked to support its passer Leela had enough time to create a passer on the king side, but not fast enough. Stockfish queened first, it was winning however Leela chose to continue. Leela tried to avoid a tablebase win, it only delayed for a few moves. Stockfish wins the game pair, it leads 3-1.

Season 21 premier division statistics

A summary statistics table of previous stages and seasons.  

Draw rate, wins

Final draw rate was 58.0%. 

Game termination

The three most common game termination causes were:

41.5% - TCEC draw rule
27.7% - SyzygyTB
24.6% - Mate

There were no crashes in the stage.

Moves per game

Median= 70.3
Average= 81.6

There were 44 games longer than 100 moves, the longest was 333 moves (AllieStein - KomodoDragon, game 149, draw). 

Time per game (hours)

Median= 2:09
Average= 2:07

Openings

There were 8-move book openings in this stage chosen by Cato. The first letter of the ECO codes was distributed as follows:

The engines had almost no freedom to choose the opening variant, all of the game pairs repeated the same ECO code and the same opening variant twice.

Reverse pairs, wins

Reverse pairs, same moves

Pairs of reverse games diverged quickly, 25.9% diverged immediately out of book, 59.8% of the pairs diverged at most after 1 move. The longest repeated sequence of moves was 15 plys (AllieStein - ScorpioNN, games 61 and 89, Modern defence, AllieStein won in white and drew in black; AllieStein - ScorpioNN, games 173 and 201, Robatsch (modern) defence, two draws) 

 

Season 21 premier division, final results

Final standings

Stockfish and Leela will play in the season 21 superfinal. In the last DRR Stockfish won 6/7 game pairs while Leela managed only 5. Leela beat Stockfish in a game pair once in the division, the only game pair loss for Stockfish, while Leela did not lose a single game pair. The reason Stockfish won the division is that it beat KomodoDragon 3 times, while Leela only managed 4 drawn game pairs.

Igel and Ethereal are relegated to league 1. Ethereal was clearly headed for relegation. Igel may have dreamed of surviving, but after it lost to ScorpioNN for the 3rd time it couldn't recover. Both Igel and Ethereal played in league 1 this season, and both were not strong enough to stay in the premier division.

AllieStein had a miserable score of -5 in the last DRR, including losses to Stoofvlees, Igel and Ethereal. For 3 DRRs it tried to keep up with 4th place Stoofvlees, in the end it was closer to 6th place ScorpioNN.

In the last DRR the top4 engines beat the bottom4 engines in 15/16 game pairs without loss, an incredible achievment, better that all the 3 DRRs before.

Interesting games 

game 169, Stockfish - AllieStein: AllieStein pushed pawns on the king side and its king was left with little pawn support. Stockfish created a central passer, there were many exchanges and Stockfish's eval increased despite giving a rook for a bishop. The game reached a RN vs RR position, Stockfish pushed its passer to the 7th rank and AllieStein's eval finally reacted. Stockfish pushed 3 passers on the king side, AllieStein saw it was lost. It gave a rook and was mated quickly.

game 170, KomodoDragon - Igel: Evals started over 1 and they increased while the engines cleared most of the queen side pawns and concentrated on the king side. The black king was threatened, KomodoDragon gave a rook for a knight and opened the king side with its queen. Igel quickly exchanged queens after KomodoDragon captured two pawns.The black king was still in danger, Igel was forced to give a rook for a knight to avoid mate. The game reached a RN vs RN position, KomodoDragon was 3 pawns up. It took 20 more moves to reach a tablebase win.

game 171, Leela - Ethereal: The center was blocked and most pawns were on the board, evals increased slowly. Ethereal was forced to move a rook and couldn't castle, Leela gave a pawn and knight for the rook. Leela then opened a file on the queen side and doubled its queen and rook there. After exchanging rooks only QRN vs QBN remained, in a series of exchanges Ethereal reduced to a QN vs Q position with connected black passers. Ethereal didn't have time to turn its passers into real threats. Leela captured a pawn and created a passer, then captured one of the black passers. Ethereal couldn't prevent a white queening, game over.

game 172, Stoofvlees - ScorpioNN: ScorpioNN moved a rook forward and grabbed a pawn on the queen side. Stoofvlees reacted on the king side and drove the black king to the center. ScorpioNN made a mistake in a complicated position with all the major pieces in the center of the board. The result was a series of exchanges that left only QB vs Q. ScorpioNN offered its queen and was mated.

game 176, Stockfish - KomodoDragon: The center was blocked and the queen side was open, evals around 1. On move 20 the engines started a long shuffle, Stockfish thought KomodoDragon's move 54 was a mistake and its eval jumped over 2. Stockfish created a passer in the center, and after exchanging queens went up a pawn and created a passer on the queen side. KomodoDragon captured the queen side passer and another pawn, by then Stockfish had a rook on the back rank. Stockfish captured a bishop and reduced to a RBN vs RN position. The black king was in a mating net, game over.

game 179, Stoofvlees - Igel: Evals were below 1 for a while, Stoofvlees' eval jumped with all the black pieces on the queen side. Stoofvlees gave a knight for a pawn and created an advanced central passer. Igel gave a bishop to capture the passer and Stoofvlees reduced to a RB vs RB position a pawn up with connected passers on the queen side. Igel couldn't stop both passers and had to lose a piece, the game reached a tablebase win.

game 180, ScorpioNN - Ethereal: Evals started around 1 and slowly increased, all the pieces were on the board and the engines opened files on the queen side. Evals were over 4 when ScorpioNN captured a rook for a knight on move 41. For a long while the engines exchanged pieces and shuffled and evals went down a little. On move 80 the game reached a RB vs BB position and evals climbed again. On move 90 there was only one white pawn left in a 7-man position. ScorpioNN did not blunder and managed to convert the win.

game 183, Stockfish - Stoofvlees: Stoofvlees seemed to be holding until move 35 with most pieces on the board, despite being two pawns down. Stoofvlees captured a pawn and exposed its king to attack, Stockfish's eval jumped over 2.  Stockfish gave a rook for two minors and attacked the black king, Stoofvlees reduced to a QBN vs QR position. Stoofvlees played almost automatically for 11 moves, its eval close to 0 while Stockfish already saw mate. Stoofvlees stopped to think and its eval jumped over 8, too late.

game 185, Leela - AllieStein: The engines castled in opposite directions, Leela's eval jumped after it took over the open h file with a rook. After it doubled rooks on the open file AllieStein gave its queen to capture one of the rooks. AllieStein had connected passers on the king side but they were not strong enough. Leela started to chase the black king and mate came quickly.

game 190, Stockfish - Ethereal: The engines castled in opposite directions, evals were around 1 without much change after the start. After a few minor piece exchanges evals slowly increased, the black DS bishiop was trapped on the king side. The engines gradually exchanged pieces until only BN vs BN remained, Ethereal was out of moves and Stockfish started to capture pawns. The game reached an opposite color bishop ending, Stockfish had enough pawns to win.

game 191, KomodoDragon - ScorpioNN: KomodoDragon's eval jumped over 2 on move 36, it gave a pawn and opened the king side. ScorpioNN only realized what was happening 3 moves later, when KomodoDragon broke through the center and offered a rook that couldn't be accepted. KomodoDragon moved the rook to the back rank, all the white pieces were involved in the attack and the black king was stuck in the center. KomodoDragon used the attack to capture pawns on the queen side, it created an unstoppable passer and promoted to a queen. ScorpioNN gave up and got mated quickly.

game 192, Leela - Stoofvlees: Stoofvlees ignored the danger to its king and tried to capture a rook for a knight. Leela's eval jumped over 6 as it ignored the knight and attacked the black king. Stoofvlees saw the danger 4 moves too late, it was a rook up but its king was in the center of the board. Leela chased the king, gaining material until it mated.

game 193, Stoofvlees - AllieStein: There were no exchanges until move 23, evals were around 1 and the engines opened the king side a little. Evals increased slowly at first, AllieStein played defensively while Stoofvlees arranged its pieces on the king side. Evals started to jump and Stoofvlees gave a rook for a knight and captured two king side black pawns. The engines reduced to a QN vs QR position, with a white passer in the center and the black king exposed. AllieStein had no escape, it lost material and was mated.

Scores after RR7:  Stockfish +17, Leela +15, KomodoDragon +9, Stoofvlees 0, AllieStein -5, ScorpioNN -7, Igel -11, Ethereal -18. At this stage the standings seem to be stable. Leela has a small chance of finishing first. AllieStein dropped away from Stoofvlees and is closer to ScorpioNN at this point.

game 202, Stoofvlees - Ethereal: The engines started a series of exchanges on move 19, resulting in a RRB vs RRN position. Stoofvlees went a pawn up before Ethereal exchanged a pair of rooks. Ethereal regained the pawn but Stoofvlees pushed a passer to the 7th rank and Ethereal gave the knight to stop it. The game continued for 20 moves and ended in a tablebase win.

game 203, Leela - Igel: Leela offered a knight on the king side, but Igel refused to take and expose its king. Leela increased the pressure on the king side and evals increased. Leela captured a rook for a bishop, then Igel finally accepted the knight and a R vs BN imbalance. Leela captured a knight and reduced to a RN vs BN position, after exchanging knights Leela had enough pawns to win

game 209, Ethereal - AllieStein: The white queen moved forward early, AllieStein gave a rook for a knight. The engines gradually exchanged pieces while evals increased, the white queen found a safe way back. Ethereal gave the material back in a series of exchanges that reduced to a QR vs QR position. The black king was exposed to attack, Ethereal chased it and captured pawns in the process. It was 3 pawns up when AllieStein gave up its pieces and was mated. First game pair win for Ethereal.

game 210, ScorpioNN - Igel: Evals were around 1 from the start, there were almost no exchanges and one open file in the center. Igel moved its queen forward and exchanged queens, ScorpioNN went a pawn up and evals slowly increased. The pieces were exchanged until the game reached a knight ending on move 58. ScorpioNN needed 20 more moves to convert the win.

game 214, KomodoDragon - Stoofvlees: See featured game below.

game 215, Stockfish - ScorpioNN: Evals were around 1 and the engines castled in opposite directions. ScorpioNN concentrated forces on the queen side, it tried to push pawns and open files. Stockfish exchanged minor pieces and created a central passer while evals increased. The white king hid behind a black pawn and Stockfish pushed the passer to the 7th rank. The white king remained safe, eventually ScorpioNN lost a bishop for the passer, it gave up its queen and got mated.

game 216, Igel - Ethereal: The engines castled in opposite directions, Igel pushed pawns on the king side and exposed the black king. Evals were over 2 on move 18, they increased for a while but then started to drift down. It seemed Ethereal stopped Igel's attack and Igel had to change its plan. On move 50 evals started to increase again, both engines were down to two pawns. After exchanging queens Igel pushed a passer to the 7th rank in a RBN vs RBN position. Ethereal started to lose material and the game ended in a tablebase win.

game 217, Igel - AllieStein: The engines castled in opposite directions, evals were over 1 and slowly increased as the engines exchanged minor pieces. Evals were over 3 when the king side started to open, a series of exchanges reduced to a QR vs QR position. Igel had a passer on the 7th rank and the black king was exposed, AllieStein couldn't hold and got mated.

game 222, Leela - ScorpioNN: Evals stayed under 1 as the engines slowly exchanged pieces. The game reached a QRB vs QRN position on move 52, then the rooks were exchanged. On move 77 the pawns stopped moving and the engines shuffled for 30 moves. Evals started increasing very slowly, ScorpioNN probably made small mistakes and Leela took over. Leela pushed a pawn to the 7th rank, and gave the bishop to promote to a queen. Mate came after ScorpioNN ran out of checks.

game 223, KomodoDragon - Ethereal: Evals started around 1 and increased a little, there were very few exchanges and the engines played behind their pawn lines. The first piece exchange was on move 30, then KomodoDragon pushed a pawn on the king side and evals started to increase. After some shuffling KomodoDragon captured a pawn on the queen side and created a passer, Ethereal was careful not to open the king side. KomodoDragon opened the g file on move 47 with winning evals, Ethereal countered by pushing a central passer to promotion. The engines reduced to a QNN vs QR position, after exchanging queens KomodoDragon had enough pawns to force a win.

game 224, Stockfish - Igel: The engines mostly shuffled from move 18, evals were under 1 until move 40. Igel saw an opportunity to grab two pawns, Stockfish's eval jumped over 3. It sacrificed a knight and opened the king side, attacking the black king. A series of exchanges reduced to a RR vs RB position. Stockfish captured pawns and gave a rook for a bishop to reach a wining rook ending two pawns up.

Featured game: KomodoDragon - Stoofvlees
Premier division, game 214
Link to game on TCEC

Evals started around 1 and didn't change for a while. KomodoDragon pushed pawns on the king side and castled long. The center was blocked and the king side partially open. Stoofvlees tried to weaken the white center pawns, KomodoDragon's eval jumped over 2 when it broke through the center with its queen and captured two pawns.

Stoofvlees thought it had a significant counter attack on the white king and its eval stayed low. It realized it was in trouble only 10 moves later, spending very little time thinking on these moves. KomodoDragon was up a piece and the black king was under pressure.

The white king was exposed but Stoofvlees did not have time to attack. It managed to get a little material back and exchange a few pieces. KomodoDragon was two pawns up with a queen side passer and the black king was not out of danger.

The black king faced a queen and two knights without pawn support. Stoofvlees moved its rook forward and attacked the white king. In desperation the black queen moved away from the king and threatened mate, this was all KomodoDragon needed to get the black king in a mating net and win. 

 

Season 21 premier division, after RR6

Standings after RR6

Stockfish and Leela continue to lead, both had 4 game pair wins in the third DRR. The gap to KomodoDragon increased a little, it only had a score of +3 in the DRR. This includes a loss to Stockfish and a double win against Stoofvlees (first black win in the division).

The bottom of the table is clearer after this DRR. ScorpioNN had a score of 0 including game pair wins against Ethereal and Igel. It is now in 6th place with a gap of 1.5 points away from the relegation zone. Ethereal will almost surely be relegated, Igel still has a chance but needs a better score and preferably a win against ScorpioNN.

Stoofvlees and AllieStein are in a private race for 4th place, AllieStein is getting closer but hasn't caught up yet and time is running out.

Game 149 between AllieStein and KomodoDragon was a long shuffle match. AllieStein would not lower its eval and the game went on for 333 moves. Not an all time TCEC record, but definitely a contender.

The top4 vs bottom4 trend continues, in this DRR top4 engines won 10/16 game pairs against bottom4 engines without loss.

Interesting games

game 114, KomodoDragon - Igel: KomodoDragon's eval jumped after Igel weakened the king side, KomodoDragon moved pieces there and opened the g file. Igel exchanged pieces until only RRB vs RRN remained, the doubled white rooks on the g file were still very dangerous. KomodoDragon gave a pawn and captured a rook for a bishop, it blocked the black passers with its king and slowly pushed the h pawn forward. Igel was forced to exchange a pair of rooks to stop the h pawn, the R vs N ending was a win for white.

game 115, Leela - Ethereal: There were very few pawn exchanges after the start and all pieces were on the board for a long time. Leela had a pawn majority on the king side, evals increased as the engines played behind their pawns. Ethereal tried to open the queen side, nothing came out of it. The engines exchanged a pair of rooks on move 38, Leela's eval was over 5. Leela pushed pawns on the king side and moved its queen forward on the queen side. Ethereal was completely paralyzed, Leela cleared the black pawns on the queen side and pushed passers forward. Ethereal gave material but couldn't prevent mate.

game 116, Stoofvlees - ScorpioNN: The center was blocked and there were no exchanges for a long time. The engines mostly shuffled, only the king side pawns stayed behind and offered some potential of a break in the pawn wall. On move 34 the engines exchanged minor pieces for the first time, the first pawn exchange was on move 48. Stoofvlees gave a bishop to create connected passers on the king side, evals started to increase when most pieces were exchanged off and Stoofvlees gave a rook to promote a pawn to a queen. The game reached a Q vs RN ending, the white queen captured pawns when Stoofvlees could avoid a check. The game continued for 30 moves, when ScorpioNN was sure it was losing it allowed a mate in 1.

game 120, Stockfish - KomodoDragon: See featured game below.

game 121, KomodoDragon - AllieStein: On move 33 KomodoDragon's eval jumped over 2, AllieStein saw the danger a move too late. KomodoDragon captured a rook for a bishop, then created a supported passer on the king side. KomodoDragon attacked the black king with its queen and pawn, AllieStein 's counter against the white king was weak. AllieStein lost more material and was mated before long.

game 124, ScorpioNN - Ethereal: The white queen moved forward and grabbed a pawn early, evals were over 1 for a long time as the engines exchanged pieces. The game reached a BN vs BN position, ScorpioNN was a pawn up with  a pawn majority on the queen side. In a series of exchanges the engines reduced to an opposite color bishops ending, white two pawns up. Unlike the usual case this position was a win for ScorpioNN.

game 125, AllieStein - Ethereal: AllieStein was a pawn up from the start. The engines exchanged pieces gradually, AllieStein created connected passers on the queen side and captured another pawn, Ethereal had an advanced passer in the center as compensation. AllieStein captured the black passer while Ethereal regained a pawn and captured one of the queen side passers. Ethereal reduced to an opposite color bishops ending, but soon regretted this since again it was a win for white. AllieStein was in no rush to finish the game, it took more than 60 moves to reach a tablebase win.

game 129, Leela - AllieStein: Leela created an advanced central passer early in the game, evals were under 1 and the engines gradually exchanged minor pieces. Leela gave a rook for a knight and moved its other rook to the 7th rank. AllieStein played a wrong rook move and lost a tempo, Leela's eval jumped over 2. AllieStein tried to expose the white king but its counter was weak. After exchanging queens Leela captured a pawn and connected a second passer. AllieStein could not stop the passers, mate followed a few moves later.

game 130, Stoofvlees - KomodoDragon: There were very few exchanges after the start, the pawn lines stabilized and the engines started to shuffle on move 30. Stoofvlees' eval was over 2, nothing happened for over 100 moves except a few exchanges and pawn moves. Suddenly KomodoDragon opened a file in the center and evals turned slightly negative. A few moves later Stoofvlees wasn't accurate and KomodoDragon's eval jumped over (negative) 2. Stoofvlees saw the danger too late, KomodoDragon reduced to a QN vs QR position and the black king couldn't escape mate. The first black win in the division.

game 133, AllieStein - Igel: Evals were under 1 for a long time with very few exchanges. Evals increased when the engines reduced to a BN vs NN position, AllieStein with a queen side passer. Igel moved its king and pieces to block the passer, AllieStein used the time to capture a pawn and create a second passer. After exchanging a bishop for a knight Igel capured one passer, but the black king was too far to help the king side pawns. AllieStein captured all black pawns and won the knight ending.

game 134, Stockfish - Ethereal: Evals started over 1 and slowly increased without exchanges, Stockfish pushed the black pieces back with its pawns. On move 31 the engines started to open the position with exchanges, leading to a RBN vs Q imbalance. Stockfish threatened the black king and Ethereal reduced to a RBN vs RN position. The black king was still in danger in the corner, Ethereal lost more material and the game reached a tablebase win.

game 140, Igel - Stockfish: Evals were over 1 from the start, the engines opened the position and evals increased. Igel gave a rook for a bishop and exposed the black king in a QRN vs QRR position. Stockfish's eval peaked over 2.5 while Igel's eval went over 4. When Igel exchanged a pair of rooks Stockfish's eval dropped to 0. Igel captured all the black pawns but after exchanging queens the game reached a tablebase draw. Perhaps a missed win for Igel.

Standings after RR5: Stockfish +11, Leela +10, KomodoDragon +7, Stoofvlees 0, AllieStein -2, ScorpioNN -6, Igel -7, Ethereal -13.

game 143, Ethereal - Leela: The game reached a BN vs BN position with white a pawn up. Ethereal's eval was over 2 and the engines shuffled. When the 50 move draw was close Ethereal exchanged knights, leaving opposite color bishops. Ethereal captured another pawn and resumed shuffling, giving 2 pawns back to continue the game. After extending the game with a pawn move on move 223, Ethereal's eval started to jump, reaching new highs while shuffling endlessly. The maximum eval was 237, very amusing for the viewers. Evals dropped to 0 as the 50-move mark approached and the game was adjudicated on move 265.

game 144, ScorpioNN - Stoofvlees: ScorpioNN captured a knight early in the game. Stoofvlees had an advanced central passer as compensation, and the white king was vulnerable. ScorpioNN kept its king safe, in a series of exchanges reduced to a QRR vs QRB position. The black king was left without support, mate was very quick. There were two white wins in this opening.

game 146, Stoofvlees - Ethereal: Evals were around 1 after the start, they increased slowly with almost no exchanges. The pawn lines stabilized and the engines mostly shuffled, until on move 52 Stoofvlees gave a pawn and opened the king side. Ethereal gave a bishop for another pawn, it had two passers on the king side, one on the 2nd rank. Stoofvlees captured one passer and exchanged rooks, after exchanging a pair of knights the game reached a BN vs N position. Ethereal was outnumbered, Stoofvlees captured all the black pawns and won.

game 147, Leela - Igel: Igel opened the queen side, then gave a rook for a knight, evals increased over 2. Leela exchanged pieces until only RN vs BB were left. Despite the black bishop pair in the open board Leela managed to capture a pawn and create a passer. Igel could have captured the rook for a bishop, probably it saw it was losing and let the rook go. The game continued for a while and ended in a tablebase win. 

game 149, AllieStein - KomodoDragon: A long shuffle game. All pawns were on the board for a long time, AllieStein gave a pawn on move 111 to keep the game going. AllieStein wouldn't lower its eval, every 50 moves it found a way to extend the game. It finally gave up and allowed to game to be adjudicated on move 333. 

game 154, ScorpioNN - Igel: ScorpioNN was up a pawn from the start with a queen side passer. There were many early exchanges and the game reached a RB vs RN position on move 29, white with connected passers on the queen side. ScorpioNN gave one passer and pushed the other to the 7th rank. Igel blocked with its knight, it took a while but ScorpioNN managed to capture all the black pawns. For a long time the engines shuffled, only on move 104 ScorpioNN started to push its second passer forward. Igel lost its rook and the game.

game 158, KomodoDragon - Stoofvlees: Evals started around 1, KomodoDragon pushed pawns on both sides of the board and the black pieces were mostly on the two back ranks. KomodoDragon broke through the center and its eval increased. KomodoDragon created a central passer and together with a bishop on e6 restricted the black pieces. The black king was in danger after KomodoDragon opened the king side and went two pawns up. Stoofvlees couldn't hold, it lost more material and was mated. KomodoDragon had a double win in this opening, the first one of the division.

game 159, Stockfish - ScorpioNN: Evals started around 1, Stockfish's eval increased after it pushed a pawn to g5. ScorpioNN's reaction weakened the black king's position on dark squares. On the queen side Stockfish created a passer supported by a bishop on d6. Stockfish went a pawn up, then in a series of exchanges the engines reduced to a queen ending. ScorpioNN saw it was losing, it gave up its queen and mate followed.

game 160, Igel - Ethereal: Igel pushed pawns and opened the king side. Evals increased as more pieces moved there, Igel doubled rooks on the g file. Then Igel pushed pawns in the center and Ethereal gave a knight to capture them, a series of exchanges reduced to a QNN vs QB position. Igel chased the black king across the board, then exchanged queens. A passer cost Ethereal its bishop, Igel had more than enough material to win.

game 166, Leela - ScorpioNN: Leela gave a knight early, but captured 3 pawns for it. There were many early exchanges and the game reached a QB vs QB position on move 26. Both kings were exposed, both engines had passers though the white ones were more advanced. Leela's eval was close to 0, but it jumped over 1 and then 2. Leela managed to move its king forward to support its pawns, then it reduced to a queen ending with a pawn up. ScorpioNN saw it was losing, it gave its queen and got mated.

game 168, Stockfish - Igel: Stockfish gave a knight for 3 pawns early, evals increased steadily as the engines exchanged pieces until only BB vs BNN were left. Igel tried to block the white pawns in the center, after a while Stockfish managed to get a pawn to the 7th rank. Igel started to lose material and mate followed.

Featured game: Stockfish - KomodoDragon
Premier division, game 120
Link to game on TCEC

Stockfish's eval was over 1 from the start, it slowly increased while the engines played with almost no exchanges. The black pieces were mostly stuck on the queen side, KomodoDragon played shuffle moves as it waited for Stockfish to take the initiative.

Stockfish pushed pawns on the king side, KomodoDragon gave a pawn and hid its king behind a white pawn. On move 33 the first minor pieces were exchanged,  KomodoDragon had a trapped rook that could only escape by taking the h pawn and exposing its king. 

Stockfish captured the black e pawn and opened a file in the center. By the time the black rook captured the h7 pawn and escaped, it turned out it was still trapped in a bigger room. Stockfish used doubled rooks in the open file to move a rook to the back rank.

Stockfish exchanged queens, KomodoDragon chose to give its trapped rook for a bishop and the game reached a RR vs RB position. Stockfish moved a second rook to the back rank and captured the remaining black pieces. It then mated a few moves later.

 

Season 21 premier division, after RR4

Standings after RR4

Stockfish and Leela are in the lead. Stockfish won 6 game pairs and lost one to Leela. Leela won 6 game pairs and drew one against KomodoDragon. KomodoDragon is still in touch with the leaders, only 1.5 points behind.

Ethereal is last after losing 6 game pairs and drawing one against Igel. ScorpioNN and Igel are candidates for relegation, so far their head to head score is a tie.

AllieStein pulled away with 3 game pair wins against the bottom engines, but it hasn't caught up with Stoofvlees yet. Both lost their game pairs against the top engines.

There were 19/28 decisive games in RR3, but only 11/28 in the RR4 reverse games. Only 4/28 game pairs had two white wins despite the opening bias. The top 4 engines beat the bottom 4 engines in 12/16 game pairs in rounds RR3-4, without loss.

Interesting games

game 57, Stockfish - AllieStein: The engines shuffled in a closed position, a few pawn moves and exchanges reset the move counter as the shuffle continued. On move 140 Stockfish's eval started to increase, with less than 20 moves left on the 50-move counter. Stockfish trapped a black rook that moved forward, then used a gap in the wall to move its pieces to the black territory. AllieStein didn't want to lose slowly, it allowed a mate in 1 on the 50th move.

game 59, Leela - Ethereal: The center was blocked, evals started to increase slowly after the position opened a little but still with most pieces on the board. After some shuffling Leela opened a file on the queen side and created a passer on the king side. Ethereal gave a bishop for two pawns to capture the white passer, the engines reduced to a RBN vs RN position. Leela blocked two black passers with its knight, after a bishop for knight trade Ethereal could not block the white passers and the game ended in mate.

game 60, Stoofvlees - ScorpioNN: Stoofvlees sacrificed a knight to open the king side, ScorpioNN built a defensive wall using its pieces and pawns and evals were low. Then ScorpioNN moved a rook forward, this gave Stoofvlees the time it needed to attack the black king and reduce to a R vs B ending. ScorpioNN could not protect its pawns, the game ended in a tablebase win.

game 61, AllieStein - ScorpioNN: The game reached  a QRB vs QRN position with white a pawn up on move 36. Evals were over 1 but for a long time it seemed ScorpioNN had a perpetual check. ScorpioNN regained the pawn and exchanged queens, the engines shuffled and gradually captured pawns. Perhaps ScorpioNN could have held, but something went wrong along the way. In the end ScorpioNN gave its knight to capture the last two white pawns, and surprisingly the result was a 6-man tablebase win in 42 moves for AllieStein in a RB vs R position with one black pawn.  

game 64, Stockfish - KomodoDragon: Evals were around 1 for a long time, Stockfish went up a pawn and it had a bishop pair advantage. After move 40 evals started to increase, the game reached a QBB vs QNN position. It appeared the engines mostly shuffled, though evals continued to increase, on move 60 the queens were off and the white bishops had a clear advantage. Stockfish captured a pawn and created a passer before KomodoDragon traded a knight for one of the bishops. It took another 20 moves to reach a tablebase win.

game 65, KomodoDragon - AllieStein: KomodoDragon sacrificed a knight and exposed the black king, then trapped and captured the black queen for a rook. A series of exchanges reduced to a QB vs RRB position, KomodoDragon gave the bishop and advanced two pawns facing the black king. The white king came forward and AllieStein couldn't avoid mate in the corner.

game 66, Leela - Stockfish: see featured game below

game 67, Stoofvlees - Igel: Evals were under 1 until move 55. The game reached a double rook ending, evals started to increase as the engines played out a long PV agreement where Stoofvlees went a pawn up and a pair of rooks was exchanged. The engines continued to capture pawns and the game ended in a tablebase win.

game 68, ScorpioNN - Ethereal: The center was blocked, evals increased while all pieces were on the board. The first piece exchange was on move 28, the engines shuffled for a while and then ScorpioNN captured a pawn and created a passer on the queen side. ScorpioNN shifted its focus to the king side, a series of exchanges reduced to a QN vs RR position. ScorpioNN captured a rook for a knight, then its queen captured all the black pawns and mate followed.

game 69, AllieStein - Ethereal: Evals increased from the start with very few exchanges. AllieStein had a space advantage, on move 44 Ethereal gave a rook for a knight to avoid further restriction to its movement. AllieStein's eval was in triple digits when the engines opened the queen side and AllieStein pushed a passer to the 7th rank. Ethereal gave a knight to stop the passer, AllieStein was a rook up in a RB vs B position but it took more than 40 more moves to reach a tablebase win.

game 70, Igel - ScorpioNN: Igel pushed pawns on the king side and exposed the black king. SCorpioNN countered with a passer on the queen side, Igel captured the passer and the black rooks moved forward. The black king was left without defenders, Igel mated using a queen sacrifice.

game 71, Stockfish - Stoofvlees: Evals were around 1 from the start with the center blocked and no exchanges. The engines shuffled for 20 moves and Stockfish's eval slowly increased. The engines opened the king side with a few exchanges, Stockfish went a pawn up and Stoofvlees concentrated forces facing the white king. Stockfish defended well, Stoofvlees gave pawns in an effort to involve its knight in the attack. The black king was exposed to attack, Stoofvlees was not fast enough in its attack. Stockfish found an opportunity to strike back and mated.

game 72, KomodoDragon - Leela: KomodoDragon's eval was over 1 from the start, it increased slowly after move 23 as KomodoDragon pushed pawns on the queen side. Leela's eval reacted a few moves later, KomodoDragon opened the queen side, gave a pawn and created a passer on the 7th rank. The black queen was trapped in front of its pawns and Leela traded it for two bishops and a knight. Leela captured the passer but lost a knight, leaving only QR vs RBN. KomodoDragon used the exposed black king to capture pawns, after exchanging rooks the game ended in a tablebase win.

game 73, Leela - AllieStein: AllieStein gave a knight and pawn in an attempt to open the king side and launch an attack on the white king. Evals increased quickly as Leela defended. AllieStein gave a second knight, Leela exchanged pieces and gave the material back to stop the attack. The result was a RBB vs RBB position, Leela captured two pawns and created a passer on the queen side. After exchanging rooks Leela pushed the passer to the 7th rank. AllieStein could not block the passer for long, it promoted to a queen and mate followed.

game 76, Ethereal - Igel: Ethereal had an eval advantage from the start, queens were off early and evals increased steadily. The engines opened the queen side and Ethereal went a pawn up. After a series of exchanges the game reached a RBN vs RR position, Igel with a pawn on the 2nd rank. Igel couldn't keep the passer, after exchanging a pair of rooks the BN vs R was a win for white. It took Ethereal another 30 moves to reach a tablebase win.

game 77, AllieStein - Igel: There were many exchanges after the start and only RB vs RB were left on move 24. After exchanging bishops Igel blundered, the engines exchanged pawns until reaching a winning 7-man position that AllieStein converted.

game 78, Stockfish - Ethereal: Evals jumped over 2 early, Stockfish gave a rook for a knight and created a 6th rank passer on the queen side. Ethereal blocked the passer, this paralyzed its queen side pieces. Ethereal was forced to give the material back, Stockfish shifted to the king side, it gave a knight for 2 pawns and exposed the black king. Ethereal gave material, then its queen gave a series of checks, but mate was unavaoidable.

game 79, KomodoDragon - ScorpioNN: Evals were over 1 from the start, the engines opened the position after a series of exchanges that started on move 17. As a result KomodoDragon was two pawns up with two passers on the queen side while ScorpioNN had a central passer. For a while ScorpioNN thought it was relatively safe, it got a pawn back and pushed its passer to the 7th rank. However evals jumped after KomodoDragon reduced to a RN vs RN position, capturing the black passer and connecting its queen side passers. ScorpioNN still managed to capture a pawn and both engines queened, but KomodoDragon made sure it would exchange queens and reach a tablebase win.

game 80, Leela - Stoofvlees: Stoofvlees gave a pawn early, evals were around 1 until Leela exchanged queens and captured another pawn with a doubled passer in the center. Stoofvlees reduced to a RRB vs RRN position, it captured the doubled passers but remained two pawns down and Leela had a passer on the queen side. The endgame was slow, Leela exchanged a pair of rooks, then it traded its passer for the last black pawn and was left with connected passers on the king side. Stoofvlees could not stop the queening and was mated.

Standings after RR3: Stockfish +7, Leela +5, KomodoDragon +4, Stoofvlees +2, AllieStein -2, ScorpioNN Igel -5, Ethereal -6. In RR3 19/28 games were decisive. Top engines beat bottom engines 8/16 times without loss, and 11/12 within group games were decisive. Stoofvlees and AllieStein now form a small middle group, both losing to top engines and beating bottom engines. The standings will be determined by the reverse games, how many of the game pairs will be decisive and how many will be double wins.

game 88, ScorpioNN - Stoofvlees: ScorpioNN had an eval advantage from the start, the engines opened the position and both had a passer in the center. Stoofvlees gave two pawns and tried to open the center and attack. Evals increased rapidly, ScorpioNN gave back the pawns and the game reached a RBN vs Q imbalance. ScorpioNN used the exposed black king to capture a bishop, then chased the black king across the board. Stoofvlees was forced to give its queen and mate followed. There were two white wins in this opening. This was the first win for a bottom engine against a top engine.

game 90, Stoofvlees - Ethereal: Stoofvlees had an eval advantage even though Ethereal captured a rook for a bishop early. Ethereal was late in developing its queen side, a series of exchanges left a RBN vs RRB position, Stoofvlees with an advanced passer. Eventually Ethereal gave a rook for the passer, after exchanging the remaining rooks Stoofvlees had enough pawns left to win.

game 91, Leela - Igel: There were no exchanges after the start. Leela's eval increased after the engines opened the position and played out a long PV agreement that resulted in a RB vs RN position with white a pawn up. Leela had a passer on the queen side still on the 2nd rank, it took a while until it was ready to push the passer forward. After exchanging rooks Igel moved its king to block the passer, leaving the king side pawns unprotected. The white king cleared the king side and the game ended in a tablebase win.

game 95, Igel - Stoofvlees: Stoofvlees gave a bishop for a pawn, it thought the open g file and threat to the white king were worth the material. Stoofvlees moved its queen forward, the white king was exposed but Igel kept it safe. Stoofvlees realized it was in trouble when Igel created an advanced passer in the center. Igel exchanged pieces and gave the material back to promote to a queen and mate. There were two white wins in this opening.

game 100, Leela - KomodoDragon: Leela's eval increased very slowly as the engines exchanged pieces and opened the position. The game reached a RRB vs RRB position on move 25, the white pieces had more freedom, the black bishop was almost trapped. Leela gave a pawn and created an advanced passer on the queen side. KomodoDragon had unsupported doubled passers, Leela captured both and two more pawns on the king side. KomodoDragon's defense crumbled, it started to lose material and got mated. There were two white wins in this opening.

game 102, KomodoDragon - Stoofvlees: Evals stayed around 1 for a long time, KomodoDragon gave a pawn but its pieces were better placed and the black king was more exposed. On move 40 KomodoDragon moved a rook to the back rank. Suddenly its eval jumped over 5, the engines played a long PV agreement and Stoofvlees thought it was very safe as it counter-attacked the white king without pausing to think. Stoofvlees was blindsighted on move 51, its king was in the center chased by the white pieces. KomodoDragon gained material and mated.

game 103, Stockfish - ScorpioNN: Evals were over 1 from then start, the engines castled in opposite directions and Stockfish pushed pawns on the king side. ScorpioNN went a pawn up but Stockfish had open files to attack the black king and the black pieces were far on the other side of the board. ScorpioNN tried to hold off the attack, it captured another pawn and a rook for a bishop. In the end there were not enough black defenders, the black king ran to the center, Stockfish gained material and mated.

game 104, Igel - Ethereal: The game reached a RRB vs RRN position with white a pawn up. One of the white pawns was doubled and black had a pawn majority on the queen side, evals were over 1. Ethereal decided to move its king to support the queen side, this allowed Igel to cut it off with a rook in the center, evals increased over 2. The white rooks came forward and eventually Igel exchanged a pair of rooks. Ethereal gave a pawn and pushed a passer to the 2nd rank, Igel controlled the promotion square with its bishop. In a series of exchanges Igel gave a rook for a knight and captured the black passer. It had enough pawns to win the B vs R ending. There were two white wins in this opening.

game 107, ScorpioNN - KomodoDragon: The center was blocked with one open file on the king side. Evals increased steadily as the engines played behind the pawn lines and occasionaly exchanged pieces. On move 78 both evals were over 4, KomodoDragon thought that white should give a pawn and attack on the king side. ScorpioNN just shuffled while KomodoDragon waited for an attack that didn't come. This went on until a 50-move draw was reached.

game 110, Leela - ScorpioNN: Leela's eval increased very slowly after the start with very few exchanges. ScorpioNN went a pawn up and tried to attack the white king. Leela kept its king safe, it trapped the forward black queen and evals increased quickly. Leela created a passer on the queen side and went up a pawn. By the time the black queen escaped Leela's PV showed mate.

game 111, KomodoDragon - Ethereal: Ethereal moved its king early and evals increased quickly. KomodoDragon used all its pieces to attack the black king and most black pieces were far on the queen side. KomodoDragon sacrificed a knight and exposed the black king, Ethereal exchanged most pieces and eventually had to give its queen for a rook. KomodoDragon mated using only its queen and pawns.

game 112, Stockfish - Igel: Evals increased quickly after the start. Stockfish attacked the black king and threatened to expose it. Igel exchanged pieces and the game reached a B vs N ending with white a pawn up. Stockfish pushed a passer on the king side and then cleared the queen side pawns with its king. The game ended in a tablebase win.

Featured game: Leela - Stockfish
Premier division, game 66
Link to game on TCEC

For 12 moves after book Stockfish moved only pawns and knights, except for one move with its queen which immediately moved back. Leela had a significant development advantage and evals increased steadily. Starting from move 21 the engines played out a long PV agreement, Leela gave a knight for a pawn to create advanced connected passers on the queen side.

Stockfish pushed its central passer to d4, but could go no further. Eventually Stockfish lost a knight for one passer and the game reached a QRB vs QRB position. Leela captured the black a pawn and created another queen side passer then it exchanged queens.

Leela captured the black passer on d2. Stockfish managed to capture the white passers on the queen side but Leela was busy on the king side and captured two black pawns there. Leela gave the rook to queen a pawn, the game ended in a tablebase win.