Season 20 superfinal games 61-70

After 70 games the score is tied 5-5 with 60 draws. Leela tied the score again though it had not been in the lead yet in the match. The last 30 games are going to be exciting. There was one game pair with a double white, the second one of the match.

Stockfish pushed pawns on the king side in game 61, Leela moved its knights there and Stockfish gave a rook and pawn to get rid of them. The white king was exposed and Leela moved its queen forward to attack. In a series of exchanges the engines reduced to a BB vs R position, Stockfish's eval went over 2. Leela moved its rook forward through the open king side, the engines traded pawns on the queen side and opened two files there. The center was blocked with the remaining 4 pawns for both engines, and Stockfish couldn't find an entry point for its pieces. Its eval only came down when the 50-move draw approached, the game was adjudicated on move 85. Did Stockfish miss a win here?

In game 62 Leela pushed pawns on the king side, Stockfish locked pawns there and did not attempt to attack. The engines opened the a file, all other files were locked by pawns except the f file. The engines exchanged a pair of rooks, then shuffled for a while with evals around 1. On move 27 Stockfish thought for 16 minutes before locking the f file as well, but its eval started to increase. The engines exchanged the remaining rooks and Stockfish's eval was over 3.

Leela arranged its pieces slowly and its eval also jumped, while Stockfish defended the open queen side and waited. On move 41 Leela gave a knight for two pawns in the center and created connected passers. It moved its knight to c6 to support the passers. When Stockfish exchanged knights Leela added a third connected passer on the c file. Leela captured a pawn on the king side, 4 passers were too many.

Stockfish lost a knight for one passer, then tried to delay with checks on the white king. When that didn't work Stockfish lost its queen and mate followed. Leela wins the game pair, the score is tied again at 4-4.

In game 63 all pieces remained on the board, the engines exchanged two pairs of pawns and opened the king side. Evals came down and the engines shuffled for a while, then in a series of exchanges the engines reduced to a BN vs R position. The pawn trades continued until there was only one pawn left for each engine, and the game was adjudicated. In game 64 the king side remained closed and the engines opened a file on the queen side. Queens were exchanged early, a series of exchanges led to a BB vs B position with Stockfish 4 pawns up and a passer on the 2nd rank. Leela had one pawn left, it could only shuffle but wouldn't lower its eval. The game was adjudicated on move 109.

Games 65-66 started with a 2-ply book 1. e4 b6, the Owen defense. In game 65 Stockfish's eval started at 1. The engines blocked the center, Stockfish had a space advantage and there were very few exchanges. The engines opened a file on the queen side and then mostly shuffled. Stockfish's eval increased to 1.5 and the engines exchanged another pair of pawns on the queen side. Stockfish tried to find a way to break through the queen side while Leela threatened the isolated pawn on b4. On move 54 Stockfish's eval was over 3 and its PV showed how it can clear the queen side and attack.

Leela decided to give a pawn and open the queen side on its own terms. Stockfish's eval jumped as it suddenly had two passers. In a series of exchanges Stockfish gave a bishop for two pawns, Leela captured one of the passers but the other reached the 7th rank. Leela lost material and stopped the passer, the game reached a queen ending with Stockfish a pawn up.

The white king was relatively protected while Stockfish had a passer on the h file facing the black king. After a while the queens were exchanged and the king and pawns ending was a win for Stockfish.

In game 66 the center remained open and the engines castled in opposite directions. Stockfish traded both its bishops for knights, this ruined the white pawn structure but gave Leela the bishop pair advantage. Evals increased as the engines exchanged pieces, they were around 3 after the queens were exchanged and the game reached a RBB vs RNN position.

The white bishops were strong in the open board. Leela created a passer on the c file and Stockfish created one on the h file. The bishops did not allow the black passer to advance, Stockfish gave a knight for two pawns to stop the white passer.

The engines exchanged rooks and the win was only a matter of time. Leela pushed a passer on the queen side and made sure the black passers on the king side could not promote. The game ended in a tablebase win just before Leela queened a pawn. There were two white wins in this opening, the score is still tied at 5-5.

In game 67 the engines locked the center and opened a file on the queen side. Both engines focused on the queen side, Stockfish doubled rooks and attacked the black a7 pawn, Leela had enough defenders. The engines shuffled for a while, then reduced to a RBB vs RBN position with equal material. Evals were low and wihtout pawn moves the game was quickly adjudicated. In game 68 the center was again blocked, this time the queen side remained closed. There were only a few minor piece exchanges after the start, the first pair of pawns was exchanged on move 17. After that the engines continued to exchange pieces until reaching a rook ending on move 29. Evals were low but there were still many pawns on the board. Both engines pushed passers forward, when they stopped moving the game was adjudicated.

Games 69-70 started with a 20-ply book in the Philidor defense exchange variation. The engines castled in opposite directions and the white queen moved forward in the center. In game 69 Stockfish pushed pawns on the king side and Leela pushed pawns on the queen side. There were no exchanges until move 22 when queens were exchanged. The engines continued to exchange pieces and pawns until the game reached a RBN vs RBN position. Stockfish was a pawn up but evals were low, the pawns didn't move and the game was adjudicated. Game 70 started similarly, the exchanges started earlier and the game reached a RRB vs RRB position on move 24. Stockfish gave a rook for a bishop and pawns, after exchanging a pair of rooks only R vs B remained and Stockfish was 3 pawns up. Evals were close to 0, Leela captured one black pawn before the game was adjudicated.

Season 20 superfinal games 51-60

After 60 games Stockfish leads 4-3 with 53 draws. Leela won its first game pair of the match, then won a second game pair and tied the score. Stockfish then regained the lead with a game pair win of its own. The opening bias increases and there were 3 decisive games in the last 10. There are 40 games left, Leela has shown in the last 10 games that anything can happen.

In game 51 the center was locked, Stockfish pushed pawns on the king side but Leela kept its king with sufficient pawn support. Stockfish castled long after a while, after exchanging queens Stockfish moved its king forward to prevent the black rook development on the a file. The engines shuffled for a while, then reduced to a RRB vs RRB position and evals came down. After trading a few pawns the game was adjudicated.

In game 52 Leela pushed pawns on the king side, it didn't castle its king though but moved it to f1 instead. Leela didn't trade pawns on the king side, it pushed a pawn to h6 and trapped a black bishop in the corner. On move 17 there was a long PV agreement, Stockfish gave a knight for pawns and opened the queen side. Stockfish stopped to think long, the PV continued to play out but Stockfish's eval jumped over 2, it wasn't happy about the outcome. The engines exchanged most pieces, Stockfish was 4 pawns up for the knight. On the other hand Leela's pieces were better placed and the black king was vulnerable.

Leela captured two pawns quickly, the white c pawn became a dangerous passer. Stockfish tried to counter by pushing two pawns in the center, however Leela took over the 7th rank and Stockfish had to protect its king. Leela gave its rook for a bishop and pushed the passer to the 6th rank.

Leela had enough resources to protect its passer and keep an eye on the advancing black pawns. Stockfish couldn't prevent a queening, Leela won material and mate followed. Leela wins its first game pair, Stockfish leads 3-2.

Games 53-54 started with a 27-ply book in the Semi-Slav defense, Meran variation, where both engines queened early and had two queens. In game 53 the engines exchanged a pair of queens, then Stockfish went a pawn up and exchanged the remaining queens. The engines reduced to a drawn rook ending with white a pawn up. Stockfish's eval was too high for the draw rule and the game continued until move 81. in game 54 Stockfish went a pawn up before the exchanges started, all queens were exchanged and the game reached a RB vs BN position with black two pawns up. Evals were close to 0, both engines pushed passers forward. Leela gave a bishop to stop a black passer, the game was adjudicated before Stockfish had to lose a bishop for a white passer.

There were no exchanges after the start in game 55, except for a pair of pawns. The engines developed their pieces and evals came down. On move 20 the engines started to exchange pieces and Leela went a pawn up. On move 41 only BN vs BN remained with Stockfish a pawn up and evals close to 0. The engines exchanged knights and were left with an opposite color bishop ending, but then Stockfish raised its eval and wouldn't lower it. The game was adjudicated only on move 180.

In game 56 Stockfish went a pawn up and traded one of its bishops for a knight. The engines exchanged queens and Leela placed a protected knight on c6. After a while Stockfish gave its second bishop to get rid of the white knight, giving Leela the bishop pair advantage. The white bishops were strong in the open center and evals started to increase. Stockfish gave a rook for one of the bishops and a second pawn, leading to a RRB vs RNN position.

Leela moved a rook to the 7th rank, Stockfish tried to counter with a passer on the queen side. Leela traded its bishop for a knight and stopped the black passer on the 2nd rank. Evals were around 3 in a RR vs RN position.

Stockfish couldn't protect the doubled pawns on the queen side and Leela captured them after a while. The white rooks started to threaten Stockfish's king and it exchanged a pair of rooks.

The remaining pawns were all on the king side. Stockfish may have hoped for a fortress but not at this level. The white king came forward and Leela drove the black knight away with its rook. The game ended in a tablebase win. Leela wins the game pair and ties the score 3-3.

Games 57-58 started with a 20-ply book in the QGD Chigorin defense, white with a bishop pair, black with two knights, and a gap in the white king side pawns. In game 57 Stockfish gave a pawn early to keep the center files closed. Leela moved its queen forward on the queen side, it captured a pawn and created a potential passer. Stockfish castled late, the engines exchanged queens and evals were close to 0. There were no pawn moves or captures and draw rule ended the game with rooks and minors on the board. Game 58 started similarly, Leela gave a pawn, Stockfish had a passer on the queen side and the engines exchanged queens. Leela didn't castle, it created a passer in the center and pushed it to the 7th rank. Stockfish pushed its passer forward and gave a rook for a bishop to block the white passer. Leela gave a rook for a knight and in the resulting rook ending both passers were captured. The game ended in a tablebase draw.

In game 59 Stockfish's eval was around 1 from the start. Leela opened the queen side and Stockfish went a pawn up. Leela tried to open a file on the king side, Stockfish refused and gave a pawn instead. It created a passer in the center, then after thinking for 19 minutes Stockfish's eval had a small jump though it played the expected move. Leela went a pawn up and thought it was safe, Stockfish's eval increased over 3.

The engines exchanged a pair of knights, Stockfish surprised Leela by playing b4 and offering a rook for a bishop. Leela thought long before accepting, it started to feel nervous and its eval jumped over 1. Stockfish predicted the sequence of moves played, the engines exchanged queens and Stockfish forked the black rooks with its bishop. This led to a RN vs RN position, Leela was still up a pawn and Stockfish with a passer on the 7th rank.

All pieces focused on the white passer, Leela couldn't move its king closer safely. After a while the engines exchanged rooks, then Leela lost its knight to capture the passer.

The endgame was slow but straightforward for Stockfish. Leela couldn't protect its pawns, the game ended in a tablebase win.

In game 60 the black queen tried to be active on the king side. Leela pushed pawns there, Stockfish moved a knight all the way from the other side of the board and sacrificed it for 3 pawns. After a few exchanges the black pawns stabilized and the engines shuffled for 20 moves. Evals came down and the engines reduced to a QN vs Q position, black 3 pawns up. Both kings were exposed to checks, when Leela created a passer Stockfish gave checks with its queen and the game was adjudicated. Stockfish wins the game pair and leads 4-3.

Season 20 superfinal games 41-50

After 50 games Stockfish leads 3-1 with 46 draws. Stockfish won its second game pair, Leela has yet to win one and half the match is over. The book exit evals are getting higher, still most of the games are draws.

In game 41 the engines castled in opposite directions. Queens were off in a series of exchanges, the king side was opened and the black king was exposed. The engines reduced to a RB vs RN position, Leela had a passer for a while but couldn't protect it. After exchanging rooks the game was adjudicated. In game 42 both engines casled short. There were only a few exchanges after the start, the engines opened a file in the center and exchanged a pair of rooks. The engines started to shuffle on move 30 and when Leela lowered its eval the draw rule ended the game.

In game 43 Stockfish pushed a pawn to h6. The black king side looked vulnerable on dark squares, yet Leela castled short. Stockfish's eval was around 1 for a while, Leela exchanged the DS bishops and felt safe. The black pawns stood in a wall across the board with a knight filling the gap on the queen side. Stockfish exchanged a pair of pawns but it couldn't break through. Evals came down, the engines shuffled and the game was adjudicated. Game 44 started with the same setup, a white pawn on h6 and black castling short. This time the engines opened the center, exchanged DS bishops and queens. Evals came slowly down as the engines continued to exchange pieces until the game reached a rook ending. The game was adjudicated when the pawns stopped moving.

Games 45-46 started with a 20-ply book in the Ruy Lopez, closed variation. In game 45 Stockfish locked the center, there were almost no exchanges and Stockfish's eval was mostly under 1. The engines opened a file on the queen side and exchanged a pair of rooks. After trading a pair of bishops Stockfish's eval came down. There were no pawn moves for a while and the draw rule ended the game, still with most pieces on the board. In game 46 again there were almost no exchanges after the start. The center was locked, Stockfish exchanged a pair of pawns on the queen side and created a passer. Leela opened the king side and threatened the black king, Stockfish exchanged queens and a pair of bishops to stop the attack. The engines started to shuffle on move 38, except for a few pawn moves. Leela's eval slowly came down and the game was adjudicated on move 84.

Games 47-48 started after all the white king side pawns moved forward, leaving the white king with no pawn support. In game 47 Leela moved its queen forward and threatened the white king, Stockfish blocked with its queen. Stockfish castled short despite an open file on the king side, Leela kept its king in the center. Stockfish blocked the open file on the king side with a knight, Leela couldn't find an entry point on the queen side. After 20 shuffling moves the engines exchanged several pieces and pawns. Stockfish gave a rook for a bishop and created connected passers that Leela had to block. In a QBN vs QRB position Stockfish gave a knight and ended the game in check repetition. In game 48 Leela moved its king forward closer to the pawns. Stockfish castled long despite an open file on the queen side. After exchanging a pair of rooks the engines shuffled for 20 moves. Stockfish had a king side passer that Leela had to watch, the engines exchanged the remaining rooks and Leela captured the passer. Evals slowly came down, the engines reduced to a QB vs QB position and the game was adjudicated.

In game 49 the engines locked the center, Stockfish pushed pawns on the king side and moved its king without castling. The engines exchanged a few minor pieces, Stockfish traded its h pawn and doubled rooks on the h file, making the black h7 pawn a target. Leela protected its pawn, evals were below 0.5 and it seemed Leela was holding as the engines mostly shuffled. Approaching move 80 both engines had less than 4 minutes left on the clock, Stockfish started to sense an advantage and its eval went over 1.

Stockfish sacrificed a knight on f5 and immediately both evals jumped over 5. Leela did not want to lose its a4 pawn so it took the knight with the pawn. This opened the way for the white g pawn to move forward, increasing the pressure on the pinned h7. Leela gave a rook to get rid of the g6 pawn. After exchanging bishops Stockfish used threats on the black a4 and d6 pawns to move its queen forward on the queen side. The black king was in danger and Leela reduced to a R vs N ending.

Stockfish created a passer on the queen side and pushed it forward. Leela had to block it, defend its d6 pawn and prevent the white king from advancing. After a while Stockfish managed to push the passer forward and Leela lost its knight to stop it, game over.

In game 50 Leela castled long and kept the king side closed. The engines exchanged a pair of minor pieces and a pair of pawns, and mostly shuffled from move 27. Evals were around 1 but Leela couldn't find a way to break through the black pawn wall. The engines exchanged a pair of knights and continued to shuffle. Just before reaching the 50-move draw Leela moved a pawn and locked the entrance on the king side. The evals came down, the engines reduced to a RB vs RB position and the game was adjudicated. Stockfish wins the game pair, it leads 3-1.

Season 20 superfinal games 31-40

After 40 games Stockfish leads 2-1 with 37 draws. After 26 draws there was a decisive game, Stockfish managed to win the first game pair of the match. The opening bias is slowly increasing, still the engines find a draw in most openings.

There were many pawn moves after the start of game 31. The engines locked pawns on the king side, a first pawn exchange on move 17 opened a file in the center. The engines exchanged a pair of rooks and evals came down. Most pawns could not move, without captures the draw rule ended the game quickly with most pieces on the board. In game 32 the king side pawns stayed back initially. The first pawn trade on move 22 exposed the black king, Leela moved its queen forward together with a pawn on g5. Leela gave two pawns and opened a file in the center, then moved a rook forward. Stockfish countered with a passer on the 7th rank, Leela regained the pawns and a series of exchanges reduced to a RNN vs RBN position. Leela captured the black passer, evals were low and the engines continued to exchange until reaching a tablebase draw.

Thefe were no exchanges in the first 35 moves of game 33. The center was locked and the engines played behind their pawn lines, Stockfish's eval fluctuated around 1. On move 36 the engines traded minor pieces and Stockfish went up a pawn, the half open file on the queen side gave Leela a target for its rook. The engines shuffled with Stockfish's eval a little higher. On move 57 Stockfish pushed f5, further restricting Leela's pieces.

Stockfish's eval slowly increased though it seemed the engines were just shuffling. The engines traded off all knights, Stockfish's eval was over 3 while Leela's eval was still under 1. Leela's bishop was trapped, it tried to attack the white weak pawn on a3 but didn't have enough attackers. Stockfish threatened the black pawn on c7 and Leela's eval started to increase. It decided to give a rook for a bishop and pawn and opened the a file, with only QR vs QB remaining.

Stockfish captured the c7 pawn, Leela finally freed its bishop but it lost another pawn on the queen side. The black king was vulnerable on the back rank, a mate threat together with an advanced passer let Stockfish capture the black bishop. Leela kept fighting but mate was inevitable. Finally a decisive game.

In game 34 the engines opened a file on the queen side early. A minor piece trade closed the file again, Stockfish pushed pawns on the king side and its eval came down to 0. However it jumped back over 0.5 when Leela moved a knight to c6. The engines opened a file on the king side and exchanged all rooks, leaving a QBN vs QBN position. After a while the engines traded B for N and opened the queen side. Leela went up a pawn but let the black queen move forward and give checks. Leela could not protect its pawns and find a safe spot for its king, evals came down and the game was adjudicated. A first game pair win for Stockfish, it leads 2-1.

Games 35-36 started with the Lasker variation of the Bird opening, From's gambit. White was a pawn up and the black center pawns were gone. Stockfish castled short in game 35 despite the open king side. Leela kept its king uncastled and threatened the king side, but couldn't break through. Leela decided to castle short as well, the engines opened a file on the queen side and exchanged a pair of rooks. Evals came down, after some shuffling the engines exchanged queens. Leela gave two pawns but pinned the white rook, a series of exchanges reduced to an opposite color bishop ending and a draw. In game 36 Stockfish castled long and its eval came down to 0 early. It sacrificed a knight and exposed the white king to attack. Leela blocked with its rook which became pinned. A series of exchanges reduced to a rook ending, evals were low and the game was adjudicated quickly.

In game 37 the engines opened the center and queens were off early. The engines continued to exchange pieces and pawns until reaching an opposite color bishop ending on move 35. Stockfish was a pawn up and wouldn't lower its eval, the game was finally adjudicated on move 146. In game 38 the center remained closed. Leela moved its king to the king side, Stockfish kept its king in the center. A series of exchanges reduced to a QR vs QRN position with white two pawns up. After exchanging queens Stockfish was down to its last pawn, evals were 0 and the game was adjudicated quickly.

In game 39 the center was locked, Stockfish pushed pawns on the queen side and Leela pushed pawns on the king side. The engines traded pawns, Stockfish opened a file on the queen side and went a pawn up, Leela threatened the white king on the king side. Leela exposed the white king with a knight sacrifice, Stockfish countered with a passer on the 7th rank, both evals were close to 0. Leela captured the passer and used a skewer to trade a bishop for a rook. The game reached a BBN vs RB position and ended in a tablebase draw. In game 40 Leela opened a file on the queen side, Stockfish was slower with its attack on the king side. Stockfish gave a pawn on the king side and opened a file, it gave a second pawn on the queen side so Leela had a passer there, but evals were close to 0. The engines traded pieces and pawns until only RN vs RN were left. Stockfish captured one pawn back, Leela pushed its last pawn to the 7th rank but could go no further and the game was adjudicated.

Season 20 superfinal games 21-30

After 30 games the score is tied 1-1 with 28 draws. The last 10 games were all draws again, the draw streak is now 24 games. We are still waiting for the book bias to be high enough for decisive games.

Games 21-22 started with the Wing gambit in the Sicilian Defense and a small bias for black. In game 21 Leela opened the center, it had a queen side passer that stayed behind while all pieces were still on the board. Stockfish gave a second pawn and opened files in the center, activating its major pieces. The black king was more exposed and this compensated Stockfish for the pawns, evals were close to 0. Leela traded its queen for the two white rooks, it pushed a passer forward and Stockfish used its queen to force a perpetual check draw. In game 22 Stockfish captured a second pawn early with its queen. Leela placed a knight on c7 and forced the black king to move, trapping the king side rook. Leela moved pieces forward on the queen side, Stockfish developed its rook through the h file and threatened the white king side. When Leela broke through the queen side Stockfish ended the game in perpetual check again.

Games 23-24 started with a 26-ply book in the King's Indian defense, orthodox variaton. In game 23 the center was blocked and all pieces and pawns were on the board. Stockfish pushed pawns on the queen side, the engines traded the first pair of pawns on move 19. Leela pushed pawns on the king side, after a few exchanges in the center the engines opened a file on the king side. The queens were exchanged and evals were close to 0, both engines thought the position was balanced. With no pawn moves the game was adjudicated on move 37, still many pieces on the board. In game 24 Leela pushed pawns on the queen side, several pawn and piece exchanges opened a file there. Evals came down to 0 and both engines preferred to keep the king side closed. The game was adjudicated on move 35, it seems both engines didn't see potential in this opening, resulting in two quick draws..

In game 25 Leela forced the white king to move early. There were many early exchanges that left only RB vs RB on move 28. Stockfish was a pawn up, the engines exchanged rooks and were left with an opposite color bishop ending. Stockfish would not lower its eval, the game was adjudicated after more than 30 shuffling moves. In game 26 both kings stayed uncastled in the center, with open files on both sides. The engines exchanged pieces until only QRB vs QRN were left on move 25. After exchanging rooks the engines avoided pawn moves, evals were low enough for an early draw rule.

In games 27-28 the black king moved right after the start, trapping the black king side rook. In game 27 the white king stayed in the center and most of the action took place on the queen side. There were many exchanges and only RRB vs RRB were left on move 27. Stockfish was a pawn up with two passers on the queen side, but evals were close to 0. Leela captured one of the passers, Stockfish finally castled on move 32. Other than that the exchanges continued and the game ended in a tablebase draw. In game 28 Leela gave a pawn and castled long. It managed to get a passer on d6, though not well supported. It took a while for Stockfish to capture the passer, by then all minor pieces were exchanged and Stockfish was still a pawn up. Leela regained the pawn and the game reached a QR vs QR position. Leela's eval was too high for the draw rule, the engines shuffled, exchanged queens, then reduced to a tablebase draw.

In game 29 the engines opened the queen side. A series of exchanges cleared the queen side pawns and left a BBN vs BBN position on move 30. Both evals were 0, the engines continued to play until reaching a tablebase draw. In game 30 the queen side remained closed, there were only a few exchanges and the engines played behind their pawn lines. Stockfish traded both its bishops for white knights, the engines started to shuffle on move 34. After 35 moves Stockfish captured a pawn, this opened a diagonal and Leela's eval increased a little. However shuffling resumed, after almost 50 moves Leela moved a pawn and lowered its eval, the game was adjudicated a few moves later.

Season 20 superfinal games 11-20

After 20 games the score is tied 1-1 with 18 draws. No change in the score after 10 straight draws. The openings are still drawish for these engines, the highest eval seen in the last 10 games was a little above 1 for a few moves by Stockfish in game 15, King's gambit accepted.

Games 11-12 started with white up a knight for 2 pawns, the white king castled and exposed. In game 11 Leela move its queen forward on the king side and castled long. Stockfish completed developing the queen side, the black queen was alone in its attack and it retreated. Leela pushed a pawn in the center, Stockfish chose not to trade it to keep the file closed and it became a passer on the 6th rank. Leela gave a rook for a bishop and pushed the passer to the 7th rank, this compensated for the material loss. The engines stopped moving pawns and the draw rule ended the game. In game 12 the white king walked to the center, Stockfish pushed pawns on the king side and castled long. Leela kept the king side closed and blocked the pawns with its king and queen. Stockfish pushed pawns and blocked the queen side, then the engines started to shuffle. After 45 moves the engines traded a pair of pawns, Leela closed the file with a knight and shuffling resumed. Leela only lowered its eval for the 50-move draw.

Games 13-14 started in the Vienna gambit and a small bias for black. In game 13 the engines opened the king side and Stockfish regained the pawn. Both engines castled long after a few minor piece exchanges. All rooks were exchanged and the game reached a QBN vs QBN position with evals close to 0 on move 23. The engines mostly shuffled for a while, then resumed exchanges that led to an opposite color bishop ending. The game was adjudicated 15 moves later. Game 14 repeated the reverse for a while, this time Leela chose to castle short in the exposed king side. Stockfish castled long, again there were many exchanges and the game reached a RB vs RN position on move 24. Evals were close to 0, the engines exchanged rooks and continued to play until the pawn moves stopped.

Games 15-16 started with a KGA Scallopp defense, again a small bias for black. In game 15 Stockfish gave a 2nd pawn temporarily, then captured 2 pawns back and equalized material. Leela castled long while the white king was exposed. The engines exchanged many pieces and the game reached a RB vs RB position, with the white king safe. Leela was up a pawn but evals were close to 0, the game was adjudicated quickly. In game 16 Leela castled immediately and Stockfish's (negative) eval increased. Leela forced the black king to move, Stockfish developed its pieces slowly. Stockfish's eval was over 1 for a few moves, then came down when it saw it didn't have a safe attack on the white king. Queens were exchanged, the engines continued to exchange pieces until only R vs BN remained. The engines mostly shuffled for over 60 moves before Stockfish lowered its eval for the draw rule.

Games 17-18 started with a 2-ply book 1. d4 f5 of the Dutch opening. Stockfish played Bg5 in game 17, Leela pushed pawns on the king side and the bishop retreated. Both engines castled short, Stockfish opened the queen side and went a pawn up with a passer on the a file. There was a series of exchanges and the net result was that Stockfish gave a bishop for 3 pawns. Stockfish gave its queen for a rook, this allowed the passer to promote while Leela captured another bishop. In the end the imbalance was R vs BB, evals were close to 0 and the engines did not move pawns so the game was cut short. Leela tried a different approach in game 18, the king side pawns stayed behind and there were many minor piece exchanges in the center. The engines opened a file on the queen side and after a while exchanged a pair of rooks. A series of exchanges led to a queen ending, Leela was a pawn up but when it started repeating the game was adjudicated.

In game 19 the white king moved forward early. Leela developed its queen side slowly and evals favored white though under 1. Leela castled and Stockfish pushed pawns on the king side. Leela remained calm, Stockfish's eval slowly came down as it did not find an effective attack. The engines shifted their focus to the center, a series of exchanges left a QRB vs QRB position with white a pawn up. Then another series of exchanges led to a drawn rook endgame. Game 20 started with a similar setup, with the white king moving forward. Stockfish chose not to castle, after a file opened in the center Stockfish moved its king to the queen side. Leela placed a supported knight on e7, the engines reduced to a QRN vs QRN position and Stockfish gave a rook to get rid of the dangerous white knight. Leela's king was exposed, Stockfish used this to give checks with its queen and the game was adjudicated.

Season 20 premier division statistics

A summary statistics table of previous stages and seasons.  

Draw rate, wins

Final draw rate was 50.0%. 

Game termination

The three most common game termination causes were:

36.2% - SyzygyTB
33.9% - TCEC draw rule
24.6% - Mate

There were no crashes in the stage.

Moves per game

Median= 68
Average= 75.0

There were 39 games longer than 100 moves, the longest was 216 moves (Ethereal - Leela, game 91, draw). 

Time per game (hours)

Median= 2:08
Average= 2:03

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

Openings were heavily biased in favor of white, there were a lot more biased 1-1 results than usual.

Reverse pairs, same moves

Pairs of reverse games diverged very quickly, 33.9% diverged immediately out of book, 77.7% of the pairs diverged at most after 1 move. The longest repeated sequence of moves was 19 plys (Leela - Ethereal, games 119 and 147, QGD semi-Slav, Noteboom variation, two draws)

Season 20 superfinal games 1-10

After 10 games the score is tied 1-1 with 8 draws. According to the explanation of the superfinal openings by Jeroen Noonen (can be found here) the openings are ordered by bias from low to high. The engines disasgreed with this order in the 3rd opening, it turned out to be biased enough for a two white win score.

Evals were essentially 0 the entire game in both games 1-2. In both games white sacrificed a knight for a pawn and black offered its rook. In game 1 Stockfish (as white) did not take the rook and preferred a pawns for knight imbalance. Queens were exchanged early, the engines continued to exchange pieces until reaching a RN vs RNN position on move 23. Leela used its knight to block the white passers on the king side. The engines traded pawns on the queen side, then the white king and rook came forward and ended the game using a mate threat and checks. In game 2 Leela as white accepted the offered rook. Its queen was trapped for a while, by the time it escaped Stockfish was attacking the white king. Leela's rook and bishop on the queen side were stuck, Stockfish exchanged the white pieces that were active and forced a perpetual check draw.

Games 3-4 started with a Q vs BN imbalance. The white king moved forward in game 3, it found safety on the king side but caused difficulty for the king side rook. Leela's eval was slightly negative despite the material disadvantage. Once Stockfish developed its rook through the h file Leela moved its king to the queen side and was focused on blocking files. The engines mainly shuffled for 35 moves, then a file opened on the king side. After exchanging a pair of rooks Stockfish moved a rook forward, then the queen joined the rook while the white king hid behind a black passer. The shuffling resumed, this time evals were low enough for the draw rule. In game 4 Leela opened a file on the queen side and let its king side rook out without trapping it. Leela used the open file to move a rook forward while Stockfish controlled the center with its minor pieces, with two knights hovering near the white king. Leela moved its major pieces forward and Stockfish used the knights to force a perpetual check draw (in the PV when the game was adjudicated).

Games 5-6 started with a 24-ply book in the Nimzo-Indian defense. The engines castled in opposite directions, white gave a rook and two pawns for a knight, white had a pawn on f6 and threatened the black king. Stockfish's eval was over 1 in game 5. Leela captured the pawn on f6 and held off Stockfish's mate threat. Leela felt safe until move 22, after thinking for 8 minutes its eval jumped over 2. Stockfish captured a bishop and the game reached a BB vs R imbalance with black a pawn up.

Evals increased gradually, Stockfish refused to trade a bishop, Leela pushed pawns on the queen side and tried to restrict the movement of the white pieces. Stockfish used its extra piece to threaten pawns and pieces and push Leela back. On move 46 the white rook came forward and captured a pawn on the queen side. Stockfish could have traded its bishop for a rook but delayed this until it traded a pair of rooks. The game reached a BN vs N position.

Stockfish captured the black a pawn and the game soon reached a 6-man tablebase win.

Game 6 started along similar lines, Stockfish captured the pawn on f6 and lost a bishop. From move 19 the engines had long agreements in their PVs and Stockfish's eval came down below 1 while Leela's eval slowly increased. The engines exchanged B for N and the white bishop pair was gone, it seemed Stockfish was holding the reverse. On move 27 Leela forked a rook and queen, still on PV. Stockfish knew how to esacpe, but it thought for 25 minutes before moving. The expected move didn't change but now Stockfish saw trouble ahead and its eval jumped over 2.

The engines continued with their expected moves, Leela almost without thinking. Stockfish's eval continued to increase as it used a lot of time to try to get away from something that bothered it at the end of the PV. After exchanging rooks Leela stopped to think for a while, its eval reacting with a small jump. The engines exchanged queens and the game reached a BN vs R position, which Stockfish was so afraid of with its eval over 4 at this point.

Now Leela took 15 minutes to assess the situation and its eval jumped over 3. It attacked the black pawns on the queen side and captured two while Stockfish tried to keep its rook active on the back rank. Stockfish created a passer on the king side and Leela captured another pawn on the queen side where it had a 3 vs 1 majority.

The black passer was Stockfish's last hope. It needed its king to support passer while it moved forward. By the time the king arrived Leela gave the bishop and queened the e pawn. The material advantage gave Leela the win a few moves later. Two white wins in this opening, score is still tied.

Evals came down quickly in game 7. The engines opened the position and exchanged most pieces, only RRN vs RRN remained on move 34. All rooks were also exchanged, Stockfish had passers on the king side and Leela had passers on the queen side. Both engines were on time to block the passers, the game reached a tablebase draw. In game 8 the position remained closed for a while with only one minor piece exchange until move 20. Evals came down, the engines opened the queen side and reduced to a RRB vs RRB position on move 29. After exchanging a pair of rooks the engines started to shuffle and the game was adjudicated.

The engines castled in opposite directions in game 9. The king side was blocked, Leela pushed pawns on the queen side facing the white king. Evals came down, Stockfish opened the center and a series of exchanged led to a RRN vs RRN position. Leela had a passer in the center, but without pawn moves the draw rule ended the game quickly. In game 10 Leela preferred to castle short, even though its king side pawns advanced and were far from its king. Stockfish opened files on the queen side and gave a rook for a knight and pawn. The black queen moved forward and with a knight sacrifice Stockfish started to give checks with its queen. Leela gave back material and was 3 pawns up for a knight, its king was still exposed. Leela pushed a passer forward and traded its queen for a rook to get the passer to the 7th rank. Stockfish ended the game in perpetual check.

Season 20 premier division, final results

Final standings

Leela and Stockfish will play in the season 20 superfinal. This was the expected result, Leela and Stockfish led the league from the start, gradually increasing the gap. In the last DRR Leela won 5 game pairs while Stockfish won only 4. The final score is a tie, their head-to-head score is a tie as well. As a result r-mobility was used to decide that Leela is the winner of the premier division. It is interesting to note that of 28 games in white Leela won 24 and Stockfish won 22.

rofChade and Ethereal are relegated to league 1. rofChade was the weakest engine of the division, it failed to win a single game pair and lost 25/28 of its games in black. Ethereal and ScorpioNN fought to survive and were only 1 point apart when the last DRR started. Ethereal's loss in white was a final blow from which it couldn't recover. Overall Ethereal and ScorpioNN had similar results: both suffered a double loss in a game pair, both lost most of their games against the top 5 engines. Ethereal beat rofChade in two game pairs and ScorpioNN in only one. However ScorpioNN beat Ethereal in their first game pair, and essentually Ethereal didn't close the gap since.

After several seasons of slow decline Komodo was updated to KomodoDragon this season and it jumped back to 3rd place above AllieStein and Stoofvlees. Recall that Komodo was close to relegation in season 19. 

There was a clear divide between the top 5 engines and the bottom 3 engines. Of the 60 game pairs played between these groups the top 5 engines won 50 and drew only 10. Three of the game pair wins were double wins.

Interesting games

Game 174, Stockfish - KomodoDragon: KomodoDragon gave a pawn and opened the queen side. Stockfish's eval increased as it shifted to the king side and opened the h file. KomodoDragon felt threatened after a white pawn reached g6, and the black king walked to the center. The black king side collapsed and Stockfish captured two more pawns. Stockfish had two passers on the king side, it traded a rook for a knight and pushed both passers to the 7th rank in a RBN vs RRB position. KomodoDragon could not avoid losing material and the game.

Game 178, Ethereal - Stoofvlees: There were many early exchanges and the game reached a queen ending on move 29. Ethereal was a pawn up and it created a passer on the queen side. Stoofvlees gave checks with its queen and Ethereal was careful to avoid a perpetual check draw. The king moved all the way forward to support a queening, and with two queens Ethereal mated quickly.

Game 183, Stoofvlees - KomodoDragon: The engines shuffled for a long while, both had very little time left. On move 71 KomodoDragon grabbed a pawn and allowed Stoofvlees to open a file on the king side and exchange pieces. The engines reduced to a BN vs BN position, Stoofvlees created a queen side passer. After a second passer moved forward KomodoDragon could not prevent a queening, Stoovflees gave a bishop but with a queen the game was over quickly.

Game 190, Stoofvlees - Stockfish: The queen side was blocked, Stockfish had a knight on the 5th rank but it was trapped. The engines exchanged all rooks through an open file in the center while evals increased steadily. Evals were over 4 when the queens were exchanged and only BBN vs BNN remained. The black pieces could hardly move, Stockfish gave its trapped knight for pawns on the queen side in desperation. Stoofvlees created a passer on the king side, Stockfish stopped it but lost its remaining pieces, game over.

Game 191, ScorpioNN - rofChade: ScorpioNN created a passer on the queen side and doubled its rooks in an open file there. rofChade gave a rook for a bishop to capture the passer and the engines reduced to a RR vs RN position. The white rooks dominated the board, ScorpioNN slowly captured pawns until it had passers on both sides of the board. rofChade blocked a passer on the queen side with its king, ScorpioNN pushed passers on the king side and managed to promote them to two queens, with mate a few moves later.

Game 192, Ethereal - KomodoDragon: The center was blocked, there was an open file on the queen side and KomodoDragon had a passer there as well, while Ethereal had a bishop pair advantage. The engines shuffled for a while, evals came down after KomodoDragon opened the king side. KomodoDragon created a passer on the king side and evals became negative. After exchanging a pair of rooks and another shuffle period evals increased and KomodoDragon pushed its passers forward. Ethereal captured the passer on the king side, opening a file for the black pieces to enter. Ethereal captured the queen side passer as well, but with a black queen and rook on the 2nd rank KomodoDragon started to capture pieces and forced a win. A rare win for black in the division.

Game 194, rofChade - Ethereal: There were no exchanges after the start, the engines shuffled with evals around 0.5. Starting from move 39 the engines traded pawns and evals increased. rofChade created an advanced passer in the center, then a series of exchanges led to a BN vs R position. Ethereal captured the white passer, for a long while it seemed that Ethereal was holding. It blocked the white king from moving forward and rofChade didn't find a way to threaten any black pawn safely. However evals kept increasing, first rofChade captured a pawn, then finally on move 108 it pushed a pawn on the king side and created a passer. Ethereal had to give its rook for a knight to stop the passer, there were enough white pawns left to win.

Game 196, Leela - Stoofvlees: There were many early exchanges and the game reached a RRN vs RRN position with evals under 1. Leela had a passer in the center that Stoofvlees blocked with its king. Stoofvlees blundered and gave a pawn so it could move a rook to the 2nd rank. This allowed Leela to push its passer to the 7th rank, only then Stoofvlees realized it was losing, 6 moves too late. Stoofvlees captured the passer but got mated by two rooks on the back ranks.

Scores after RR7: Leela +18, Stockfish +17, KomodoDragon +9, AllieStein +4, Stoofvlees -2, ScorpioNN -12, Ethereal -14, rofChade -20. Leela still leads by 0.5 points, 4 of its remaining games are with white. Stockfish has only 3 white games left, unlikely that it can catch up. Ethereal is still only 1 point behind ScorpioNN, its losses to rofChade and to KomodoDragon playing white were hard blows. It also has only 3 white games left, its best hope is to win the one against ScorpioNN.

Game 197, AllieStein - Stoofvlees: The game reached a RB vs RN position, AllieStein saw something that Stoofvlees missed and its eval jumped over 4. It took 13 moves for AllieStein to go a pawn up with the queen side pawns gone except one white passer. AllieStein moved its rook to the 7th rank while its king came forward. The black king could not move out of the back rank, the black pieces were too far to help and AllieStein captured all the black pawns on the king side. AllieStein was 3 pawns up and clearly winning, but it was in no hurry and the game continued for more than 50 moves before reaching a tablebase win.

Game 205, AllieStein - ScorpioNN: AllieStein had a passer in the center with the queen side clear and a Q vs RN imbalance. The engines reduced to a Q vs RB position and ScorpioNN gave its bishop to capture the white passer. The resulting 7-man position was a tablebase win for white, but slow with long term planning necessary. AllieStein wasn't able to find the correct move sequence in time and the game ended just before the 50-move draw.

Game 207, Leela - KomodoDragon: see featured game below.

Scores with 3 rounds remaining: Leela +20, Stockfish +19, KomodoDragon +8, AllieStein +5, Stoofvlees -2, ScorpioNN -13, Ethereal -16, rofChade -21. Leela still leads Stockfish by 0.5 points. Ethereal only managed a draw against ScorpioNN, it is now 1.5 points behind and is very likely to be relegated.

Two rounds to go. Ethereal lost to AllieStein and ScorpioNN held against KomodoDragon, Ethereal cannot survive even theoretically since ScorpioNN has a tiebreak advantage. Leela and Stockfish drew their head to head game, their final head-to-head score is a tie with one game pair win each.

Game 218, Stockfish - Stoofvlees: Stockfish pushed pawns on the king side, its eval jumped over 3 after Stoofvlees gave a rook for a bishop. The king side opened and both kings were exposed to attack. Stockfish pieces were better placed and its attack was quicker. Stockfish captured a knight and the black king was caught in a mating net. Two white wins in this opening.

Leela drew against AllieStein, going into the last round Stockfish and Leela are tied for 1st place.

Leela and Stockfish drew their last games. The r-mobility tiebreak was used to decide that Leela won the premier division.  

Featured game: Leela - KomodoDragon
Premier division, game 207
Link to game on TCEC

Leela was up a rook for a bishop and pawn early in the game. Leela controlled an open file in the center, KomodoDragon had advanced pawns on the queen side and its pieces were active there. Evals were around 1 when KomodoDragon moved its queen forward to capture a pawn. Leela used the fact that the black queen was far to attack the back rank. After move 24 it thought for 7 minutes though KomodoDragon's last move was expected in both PVs.

Leela's eval jumped over 3, it changed its PV move to a knight sacrifice on g6. The black king was exposed and after exchanging a pair of rooks Leela's remaining major pieces moved forward. KomodoDragon reduced to a R vs BN position to avoid a back rank mate.

The white rook kept the KomodoDragon's king away from the pawns. The black pieces protected the queen side pawns and Leela went after the pawns on the king side. The engines traded a few pawns and KomodoDragon lost the pawns on the king side, Leela went two pawns up with two passers.

KomodoDragon kept its bishop on the diagonal protecting a7, its king came forward to block the white king. Leela then pushed the h pawn and sacrificed its rook to promote it to a queen. The game was over not long after that.  

Season 20 premier division, after RR6

Standings after RR6

Stockfish and Leela continue to lead. In the 3rd DRR Leela had 6 game pair wins, including the one against Stockfish. Stockfish had only 5 game pair wins and one loss. As a result Leela is only 0.5 points behind and the race is on for 1st place. It is clear that these will be the finalists in any case.

The gaps between the engines in places 3-5 have increased a little. KomodoDragon had a great score of 5 game pair wins and one loss in this DRR, its 3rd place appears more firm.

ScorpioNN and Ethereal continue their race to survive in the division. ScorpioNN is slightly ahead but it is far from safe. There were two white wins in their direct encounter this DRR.

Interesting games

Game 125, AllieStein - Stockfish: The game reached a double rook ending and Stockfish's eval was 0. On move 34 Stockfish's eval jumped over 6 after thinking for six and a half minutes, despite the fact that AllieStein played the move Stockfish expected. The eval went over 8 for the next two moves, then dropped back to 0 after AllieStein's move 37. There may have been a deep win for white that AllieStein missed here. The engines reduced to a drawn rook ending.

Game 128, ScorpioNN - Ethereal: Evals constantly increased as the engines exchanged pieces. The game reached a RBB vs RBN position, ScorpioNN's eval advantage was probably due to the bishop pair. After exchanging the rooks ScorpioNN captured a pawn, then used its queen side pawn majority to create a passer. Ethereal had to block and ScorpioNN had time to move its king forward and to capture all the remaining black pawns. The game ended in a tablebase position.

Game 131, rofChade - Stoofvlees: Stoofvlees gave its queen for two knights early. For a while Stoofvlees thought its attack on the white king gave it compensation, but when it sacrificed a knight there were not enough pieces left for the attack. rofChade shifted to the king side and attacked the black king, Stoofvlees was not prepared for defense and it got mated.

Game 133, AllieStein - Leela: AllieStein was sure it was winning in a double bishop ending with a passer on the 6th rank. Leela managed to prevent the passer's advance, the engines shuflled for 130 moves before AllieStein realized it cannot win and lowered its eval. Leela captured the passer on the 7th rank and the game was adjudicated on move 204. Did AllieStein miss a win? Perhaps it should have avoided some of the early exchanges.

Game 135, ScorpioNN - rofChade: The engines shuffled for a while in a RRN vs RRB position. After exchanging a pair of rooks ScorpioNN started to capture the black pawns until they were all gone. ScorpioNN had connected passers in the center that gave it the win. 

Game 137, KomodoDragon - AllieStein: KomodoDragon started an attack on the king side with a bishop sacrifice. After a series of exchanges only R vs BN remained on move 25. The engines traded pawns until there were only two white pawns left in a 7-man position. KomodoDragon managed to convert by slowly pushing a pawn to the 7th rank, then forcing AllieStein to lose a piece when the second pawn moved forward.

Game 140, Leela - Stoofvlees: Leela had an advanced passer on d6. It gave two pawns and cleared the squares surrounding its passer, then moved its rook and queen to the 7th rank. Stoofvlees exchanged queens and Leela thought that was a mistake. Leela pushed its passer with two rooks on the 7th rank, Stoofvlees tried to counter with pawns on the other side but was too late. Leela captured a rook for the passer and mate followed.

Scores after RR5: Stockfish +13, Leela +11, KomodoDragon +7, AllieStein +2, Stoofvlees -2, ScorpioNN -7, Ethereal -9, rofChade -15. 

Game 141, AllieStein - Stoofvlees: Evals slowly increased though material was equal, on move 28 AllieStein captured a pawn and created an advanced passer in the center. The black pawns were all isolated, before long AllieStein captured them all. The engines reduced to a double knight ending, the 3 white pawns ensured AllieStein would win though the game continued for almost 50 more moves.

Game 149, AllieStein - ScorpioNN: ScorpioNN blundered in what appeared to be a drawn position. It chose to reduce to a king and pawns position and realized it was lost two moves too late.

Game 151, Leela - KomodoDragon: Evals were around 0.5 and the engines shuffled for a long while. Things started to go wrong for KomodoDragon when it pushed a pawn on move 63. Evals increased slowly at first as the engines opened the king side and Leela pushed pawns on the queen side. KomodoDragon went up a pawn, Leela hid its king behind a black pawn and created a passer on the queen side. Leela then reduced to a RN vs RB position, it lost its passer but captured 3 black pawns. Leela pushed its remaining pawns forward and forced a queening to win the game.

Game 153, Stockfish - AllieStein: AllieStein kept its king in the center with open files on both sides. AllieStein didn't see the danger until its king was exposed and forced to move. Stockfish lost some material in a counterattack, the game reached a QRB vs QRR position with white two pawns up. The black king found safety in the corner while Stockfish slowly pushed passers on the other side. AllieStein could not stop the pawns and when it ran out of checks Stockfish queened, with mate following.

Game 155, KomodoDragon - Stoofvlees: KomodoDragon's eval jumped over 2 early as it attacked on the king side. Stoofvlees castled long so its king could escape but it lost a bishop. Stoofvlees had some compensation since it pinned a knight and the threatened white queen had to defend or lose it. KomodoDragon found a way to free the pin without losing material. Stoofvlees tried a desperate attack on the white king, but couldn't avoid mate.

Game 156, Ethereal - ScorpioNN: The black king moved early and hid behind a white pawn. Ethereal sacrificed a knight and opened a file on the king side, its eval jumping to 4. Ethereal soon had a strong attack on the black king, scorpioNN gave a rook for a bishop to reduce the number of pieces attacking. However the black king was targeted by all major white pieces, a series of exchanges led to a Q vs N ending and a win for Ethereal. Double white wins in this opening.

Game 160, Leela - Stockfish: Stockfish gave a rook for a knight early in the game, this weakened the white queen side where Leela's king was located. The black king remained uncastled, however both engines did not have an effective attack. Evals increased as the engines exchanged pieces, the game reached a RN vs BN position. The endgame was slow, after 15 moves the engines reduced to R vs N ending, Leela created an unstoppable passer after another 15 moves. Mate followed not long afterwards.

Game 161, Leela - AllieStein: see featured game below.

Game 162, Stockfish - Stoofvlees: After some preparation Stockfish broke through the center. After a series of exchanges Stockfish was a pawn up and the center was clear, the black king exposed to attack by the white major pieces. The game reduced to a QRR vs QRR position and Stockfish took over the 7th rank with two rooks. Stoofvlees started to lose material and mate came in a few moves.

Featured game: Leela - AllieStein
Premier division, game 161
Link to game on TCEC

Evals were under 1 after the start, Leela pushed pawns on the queen side which was mostly blocked. AllieStein moved its queen forward on the king side and pushed pawns facing the white king. On move 18 AllieStein exchanged a forward white bishop with a knight, which created a passer for Leela on the 6th rank. There was a 20-move PV agreement, at the end of which was a QBN vs QR position. However AllieStein changed its mind and sacrified a bishop to open the king side instead. It thought it had a strong attack on the white king, Leela was certain it was safe and its eval jumped over 2.

Leela played f3 to prevent the black knight move to g4, while on the other side Leela moved a knight to b5 and suddenly the isolated passer became a serious threat. AllieStein ignored the threat to its rook on a7, it continued to add more pieces to the attack and its eval remained under 1. Leela captured the rook, AllieStein expected something else and suddenly its eval changed to a mate prediction for white.

AllieStein realized its attack wasn't fast enough and it was forced to keep an eye on the white passer. Leela's counter was very quick. The g file opened and Leela exchanged a pair of rooks. Then the d file opened, the white queen came forward and it mated together with a knight.

Season 20 premier division, after RR4

Standings after RR4

Stockfish and Leela continue to lead the division, extending their lead slightly. There are 28 more rounds to play so anything can still happen, but it seems probable that they will play in the superfinal. Stockfish won 6/7 game pairs in the second DRR, including wins against Leela and KomodoDragon. Leela also won 6 game pairs, but lost one to Stockfish. It is interesing to note that so far Stockfish has won 12/14 games in white, while Leela won 13/14.

KomodoDragon, AllieStein and Stoofvlees are close together in places 3-5. Stoofvlees dropped to 5th place after a weak DRR with 3 game pair losses and only one win.

rofChade continues to accumulate losses and is last, probably heading for relegation. ScorpioNN and Ethereal are trying to avoid 7th place, this appears to be the closest race in this division and the result is hard to predict.

Interesting games

Game 62, Stockfish - KomodoDragon: Evals gradually increased though material was equal. KomodoDragon had two isolated pawns on the queen side which had to be defended, and Stockfish had a bishop pair advantage. On moves 54 and 58 the engines traded a pair of pawns and both created passers on the queen side. KomodoDragon tried to open the king side, this only exposed its king to attack. Stockfish quickly shifted to the king side and captured a knight. KomodoDragon couldn't deal with the advancing passer and the threat to its king, both engines saw the mate coming.

Game 66, Ethereal - Stoofvlees: A series of early exchanges reduced to a rook ending. Both engines created a passer on the queen side, Stoofvlees blocked its own passer with the rook while Ethereal had an open path forward for its passer, supported by the king. The game ended a few moves after Ethereal queened its passer.

Game 71, Stoofvlees - KomodoDragon: After the start the engines mostly played behind their pawn lines with only a few exchanges, evals increased slowly. On move 40 Stoofvlees created a passer by a pawn trade. KomodoDragon opened a hole in the pawn wall on the king side, then blocked it with a bishop that couldn't move. After a period of mostly shuffling Stoofvlees moved its king toward the center and evals jumped. KomodoDragon gave a pawn and opened a file on the queen side, then traded its bad bishop for a knight. Only major pieces remained, Stoofvlees finally pushed its passer on move 96. It captured a second pawn and reduced to a rook ending two pawns up, enough for a win.

Game 76, Stockfish - Leela: see featured game below.

Game 81, KomodoDragon - AllieStein: The center and queen side were blocked except for the open a file, KomodoDragon with a space advantage. AllieStein gave a pawn to get more space on the king side. KomodoDragon took over the a file with a rook exchange and moved its remaining rook forward. The game reached a QRB vs QRN position, KomodoDragon gave back a pawn to open a file on the king side and threatened the black king on light squares. The white queen moved forward, KomodoDragon gave its rook for the knight and captured 4 pawns. AllieStein couldn't stop the white passers, lost its rook and the game.

Game 84, Leela - Stoofvlees: Leela captured a pawn and created a queen side passer, Stoofvlees blocked it with a rook. The engines exchanged pieces and evals increased, in a QRB vs QRN position Leela abandoned the passer but took over the back rank. It chased the black king all the way to h3, Stoofvlees gave material but only delayed the mate.

Scores after RR3: Stockfish +8, Leela +6, KomodoDragon +3, Stoofvlees AllieStein +1, ScorpioNN Ethereal -5, rofChade -9.

Game 85, AllieStein - Stoofvlees: A long PV agreement starting from move 14 led to a QB vs RRN imbalance. Both engines moved pieces forward and captured most of the pawns on the queen side. AllieStein's eval increased to around 2 and then Stoofvlees blundered and evals jumped. The black king was in danger, and the two black rooks on the 2nd rank were too far to help and too late to counterattack. AllieStein exposed the black king and mate followed. 

Game 95, Leela - KomodoDragon: Evals were under 1 until move 36. Material was equal and Leela's advantage was not obvious, perhaps a better pawn structure, or better piece arrangement. Evals continued to increase, KomodoDragon traded a bishop for a white knight in the center and the engines reduced to a BB vs BN position. The bishop pair was strong and Leela went two pawns up, it had enough pawns left to win.

Game 97, Stockfish - AllieStein: Evals stayed around 1 for a long time. The engines opened a file on the queen side and AllieStein kept a rook there. After a period of mostly shuffling Stockfish gave a rook for a bishop and pawn and the position opened up. Then there was a series of exchanges that followed a long PV agreement, reducing to a RBB vs RR position with black two pawns up. Stockfish's eval jumped after AllieStein pushed its pawns too far in Stockfish's opinion. AllieStein allowed a bishop for rook trade, perhaps thinking that the RB vs R ending would be a draw with only one white pawn left. It soon realized its mistake as Stockfish patiently moved its king forward and threatened mate. AllieStein could only delay it for a few moves by giving the rook.

Game 99, KomodoDragon - Stoofvlees: The engines exchanged minor pieces and evals increased slowly. The black king was partially exposed and KomodoDragon moved pieces to the king side. Stoofvlees gave a rook for a knight and pawn, maybe it hoped its bishop pair would help in defending the king. Komodo continued to attack, with one rook on the 7th rank and its queen on the king side the black king was soon in a mating net. A double white win in this opening.

Game 105, Leela - AllieStein: AllieStein gave a knight for pawns and created connected passers on the queen side. In a RBB vs RB position Leela attacked the passers with a bishop and AllieStein moved its rook to defend in front of the pawns. Leela thought this was a mistake, it quickly trapped the rook. The black bishop tried to help and got trapped as well. Leela used its pawns and extra bishop to create a passer and AllieStein could not stop it. The passer queened and mate followed.

Game 106, Stockfish - Stoofvlees: Stoofvlees captured a pawn and Stockfish's eval jumped, it immediately reacted with a knight fork and captured a rook for the knight. Stoofvlees was confident it had enough compensation as it attacked the exposed white king. Only 15 moves later Stoofvlees realized Stockfish had a way out. The attack ended in a queen ending, Stoofvlees captured two pawns but Stockfish's last pawn was an unstoppable passer. Stockfish quickly mated in a QQ vs Q position. 

Game 110, Ethereal - rofChade: Ethereal's eval jumped after the queen side opened. rofChade had a passer on the queen side but also an isolated pawn in the center. After exchanging queens Ethereal took over the center and moved a rook to the 7th rank. rofChade exchanged a pair of rooks and reduced to a RB vs RN position. Ethereal captured a pawn, then blocked the passer and continued to capture black pawns until there were none left. The game ended in a tablebase win a few moves later.

Featured game: Stockfish - Leela
Premier division, game 76
Link to game on TCEC

Stockfish castled long and Leela kept its king in the center. Leela moved its queen forward on the queen side and started to push pawns facing the white king. Stockfish offered a knight for two pawns, Leela chose to leave the knight and attack the white king. Stockfish captured a rook, Leela's queen and bishop pair looked scary but Stockfish was confident it can survive the attack.

Leela chased the white king to the center and Stockfish had to give back material. Stockfish exchanged pieces and the attack was over in a RB vs RB position, white a pawn up with a passer on the 7th rank.

Stockfish avoided an opposite color bishop ending, it gave up the b7 passer and moved its king forward to support the pawns on the king side. The engines traded pawns until only 2 vs 1 remained.

Stockfish pushed 2 passers forward supported by its king, while its rook controlled the 7th rank. Leela started to lose its pieces and the game ended.