Season 21 superfinal statistics

A summary statistics table of previous stages and seasons. 

Draw rate, wins

 

Final draw rate was 74%.

Game termination

The three most common game termination causes were:

65% - TCEC draw rule
17% - SyzygyTB

15% - Mate

There were no crashes in the stage.

Moves per game

Median= 65
Average= 73.8

There were 13 games longer than 100 moves, the longest was 217 moves (Stockfish - Leela, game 68, Stockfish won).

Time per game (hours)

 

Median= 3:58
Average= 3:52

Openings

There were variable length book openings in this stage chosen by Jeroen Noomen and GM Matthew Sadler. The first letter of the ECO codes was distributed as follows:

The engines had almost no freedom to choose the opening variant, all the games repeated the same ECO and the same opening variant twice.

Reverse pairs, wins 

Reverse pairs, same moves  

Pairs of reverse games diverged much slower than usual, 12% diverged immediately out of book, 40% of the pairs diverged at most after 1 move. The longest repeated sequence of moves was 13 plys (Leela - Stockfish games 93 and 94, French Winawer (Nimzovich) variation, Stockfish won as white). In fact, the divergence on ply 14 transposed back and the second divergence was after 22 plys. 

 

Season 21 superfinal games 91-100, season summary

Stockfish wins the superfinal of season 21, the final score is 19-7 with 74 draws. In the last 10 games there was one game pair with two white wins and then Stockfish won 3 more game pairs and extended its lead. 

The openings of the superfinal were not ordered by their expected bias as in season 20. The order was not random probably, for example the 3 game pairs with black advantage were consecutive. This season the openings were prepared by Jeroen Noomen and GM Matthew Sadler, each responsible for half of the openings. Stockfish led from the start, the gap was small at first and was only +3 after 50 games. Then Stockfish won 6 game pairs in the next 20 games, Leela won only one and the gap increased to +8. Leela won a game pair in the next 10 games, but in the last 20 games Stockfish extended its lead with 5 more game pair wins. Only two openings resulted in two white wins. 

There were many games that Stockfish won, where the eval turning point followed an "instamove" in which Leela spent very little time thinking and used its prepared PV to play. Usually Leela was surprised by Stockfish's reply, it spent a lot of time thinking on its next move and its eval jumped as well. I don't know what would have happened if Leela thought more on the crucial move, but improving its time management or forward search may make it better. 

This season there were a total of 46 engines participating. The lower leagues of the season were short 1DRR events that flew by as always. Booot and Nirvana returned to TCEC after not participating for a few seasons. Nirvana climbed to league 4 and then was relegated back. Booot together with ClassicAra made it to league 2, there Booot stayed and ClassicAra was relegated to league 3. Koivisto, a new non-crashing version, also started in qualification and ended in league 3. Halogen started in league 4 and ended in league 2. League 1 was a more serious 2DRR affair, none of the lower league engines could get there. The league 2 qualifiers were veteran engines Nemorino and Pedone, Nemorino was then relegated back. The second relegated engine from league 1 was rofChade, a bit surprising since it qualified for the premier division in season 20. The qualifiers for the premier division were Ethereal, same as in season 20, and Igel, first time appearance.

The premier division was a 4DRR event. Stockfish and Leela took the lead early and qualified for the superfinal. Stockfish won the premier division despite the fact that Leela beat it in one game pair. Leela was the only engine that did not lose a single game pair in the division. KomodoDragon continued its success of season 20 and finished in 3rd place, not too far behind. Ethereal and Igel were relegated back to league 1.

A new addition in the superfinal of this season was the live commentary of some of the games by GM Matthew Sadler, author of half of the opening. This is something that was missing in TCEC from the start, a real expert that can analyze the games as they are played and share his opinions. GM Sadler has a lot of respect for the engines, in his commentary he refers to the plans they have in their PV, and gives his understanding of the game in terms a layman like me can understand. I listened in to only a few of these live streams, I get overloaded during the superfinal since I write a summary of every game, and I can't keep up. I use the archive to follow the games and don't have a lot of time for the live ones. Now that the season is over I will go back and look at a few selected videos for games I thought were interesting.

During the season I heard that Guy Haworth had died, I mentioned this in my league 1 summary. Guy Haworth wrote the season summaries that appear in the TCEC articles tab, together with Nelson Hernandez (Cato). He was a reader of this blog, and left me a few comments and corrected my errors. We communicated briefly during season 20, sadly he died before we had a chance to discuss this season.

A final word on the Covid pandemic. It's been 6 months since I wrote the summary of season 20, Covid is still here. The virus keeps finding ways to improve, the delta variant is spreading fast, much faster than the original. Us humans have to keep ourselves as safe as possible, especially those of us who are not so young anymore. My message from the last two seasons is still valid:
"Please take this seriously, avoid crowded places and unnecessary contacts. Keep yourselves and your family safe. Governments may give bad advice or act slowly, but our personal health depends mostly on our personal behavior."
To this I can add: if you can, get vaccinated. The vaccines are safe and they lower the threat of getting infected significantly. Apparently the vaccines are less effective against infection by the delta variant, but still they lower the chance of a severe disease or worse. Getting vaccinated is important for you as well as your loved ones, even if you are young and Covid is less of a threat to you. Please, get vaccinated if you can.

That's all from me this season, hope to be here for the next one.

Go TCEC!!

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Games 91-92 started with a 26-ply book in the KID Orthodox variation, that diverged from recent GM games at the 26th ply. In game 91 Leela pushed a pawn to a6 and Stockfish exchanged it. Stockfish's eval was over 1.5, the engines shuffled for a long time with one minor piece exchange that created an advanced passer for Leela on the queen side. On move 46 Stockfish opened a file on the king side and went a pawn up, creating a central passer. Stockfish gave the pawn back on the queen side where Leela added a second passer. On move 52 the queens were exchanged.

Stockfish pushed the h pawn forward, connecting a second passer when Leela captured the h pawn. Leela blocked the black passers and Stockfish didn't have the strength to support them. Stockfish exchanged a pair of rooks and captured one of the queen side passers, it tried to block the second one.

The black knight and bishop couldn't support each other and the remaining pieces were too far away. Leela's rook drove the defenders away and pushed the passer to the 7th rank. Stockfish managed to capture the passer but lost its rook. The h pawn was unstoppable, Leela queened and then mated.

In game 92 Stockfish pushed the a pawn forward, when it reached a6 Leela played b6 instead of taking it. There was one pawn exchange on the king side, no exchanges besides that. Stockfish's eval was over 2.5, but it seemed to be shuffling from move 21. The white king walked to the queen side, evals slowly drifted down. On move 56 evals started to increase again, Stockfish waited for the right moment and on move 68 it pushed h4.

Stockfish opened the h file and the exchanges began. The black king became exposed, and after clearing most pawns from the king side the white g pawn became a dangerous passer. Leela preferred to give a rook for a bishop to capture the passer.

Material seemed balanced but Leela couldn't prevent the white queen moving forward. Stockfish captured two black pawns, it gave the rook but captured the bishop. Material was equal again but two advanced passers on the queen side were strong enough to secure a win. There were two white wins in the game pair, Stockfish leads 16-7.

In game 93 there were many early exchanges on the queen side and only RRN vs RRN remained on move 20 with white a pawn up. The engines gradually exchanged pawns and evals came down. Leela had two advanced passers on the queen side, Stockfish countered by doubling rooks on the 2nd rank and threatening the white king. Leela exchanged a pair of rooks and gave up one passer to secure its king, the 7-man position was a draw and the game was adjudicated.

The engines repeated 21-plys of the previous game in game 94 up to transpositions. Stockfish's eval was over 1, the queens stayed on the board longer than in the previous game. From move 20 the engines played out a PV agreement, Stockfish gave a pawn in the center while its knight moved to the central e5, Leela moved a rook to the 2nd rank. Stockfish regained the pawn on the queen side and created an advanced passer, Leela doubled rooks on the 2nd rank and threatened the white king. Leela was surprised by Stockfish's move 29, it thought for 13 minutes and its eval jumped to around 1. Stockfish moved its queen forward on the king side, captured a pawn and then exchanged queens.

The game continued in a long PV agreement with evals slowly increasing. The engines traded pawns, Leela kept the pressure on g2 and Stockfish made sure it was protected. By move 45 there were only two white pawns on the king side and one black pawn on the queen side. Leela abandoned the 2nd rank and moved its pieces to protect its last pawn and push it forward. Knight were exchanged on move 54 and the game reached a double rook ending. 

Stockfish played the ending very patiently, alternating between harassing the black king and slowly pushing its own passers forward. Leela defended the best it could, by move 80 it only managed to move its passer to b4 while Stockfish had a passer on h7. Leela traded pawns and this left a 7-man position with one last white pawn. The game ended in a tablebase win. Stockfish wins the game pair, it leads 17-7.

In game 95 the center was blocked and the engines opened two files on the queen side. After a few exchanges in the center all rooks moved to the queen side. The engines played out a long PV agreement, evals came down and all rooks were exchanged. On move 39 the game reached a QN vs QB position, both kings were exposed to checks. Leela wouldn't lower its eval, a few pawn trades extended the game which was finally adjudicated on move 95.

In game 96 there were two pawn exchanges after the start, one on each side, but no files were opened. The engines mostly agreed in their PVs and evals did not change a lot. On move 26 Stockfish captured a pawn on the king side and created a passer there. Leela did not want to open files close to its king and it allowed Stockfish to push a second passer forward. Leela captured a pawn on the queen side and created a passer of its own. On move 35 the engines exchanged queens.

 

Not a lot happened for a while, both engines pushed their passers forward and both blocked their opponent's passer. Leela used its king and a knight to block the white passers on the king side, effectively trapping its own king. Stockfish's eval started to increase, its king walked to the queen side to block the black passer there and free a knight to join the attack on the king side. Evals jumped quickly, they were over 6 when Stockfish surprised Leela and offered a bishop on move 57.

Leela couldn't take the bishop because of immediate mate. Instead it captured the knight on e6, this started a series of exchanges that opened the king side and led to a R vs N position on move 69. The rook was much stronger than the knight in an open position, Stockfish managed to queen a passer and win. Stockfish wins the game pair, it leads 18-7.

In game 97 there were no exchanges after the start and the engines played behind the pawn lines, the black king walked to the king side without castling. On move 19 Leela gave a pawn and opened the center. Stockfish managed to connect its rooks on the back rank, Leela regained the pawn and created a passer on the queen side. After a few pawn moves and a minor piece exchange the engines started to shuffle. On move 51 Stockfish's eval dropped to 0, it gave a pawn and captured a rook with its bishop. Leela had an advanced passer on the king side, it chose not to retake and instead to attack the black king. Eventually Leela captured back a rook, but then Stockfish ended the game with a repetition draw.

In game 98 Stockfish exchanged both bishops for a bishop and a knight early. Stockfish's eval was over 2 and increasing, the black queen came forward and was a target for attacks. Leela castled its king and found a way for the queen to retreat. Stockfish pushed pawns on the king side, it gave a pawn to create an opening in the pawn wall protecting the black king.

All the white pieces moved to the king side, Leela surrounded its king with pieces and tried to hold on. Stockfish moved its queen slowly, in small steps, through the h file opening and all the way to h7. Leela could only watch and wait, while making sure its king had a path to get out of the corner.

Stockfish planned its attack very carefully, Leela saw the same sequence of moves in its PV. There was a series of exchanges that resulted in a QR vs QN position, then Stockfish just reduced to a king and pawns ending. It was a pawn up, Leela couldn't prevent a queening and mate was just a matter of time. Stockfish wins the game pair, it leads 19-7.

In game 99 Stockfish gave a pawn in the center and the engines opened a file. Stockfish castled long and pushed pawns on the king side. Evals did not change a lot as the engines exchanged minor pieces and Leela kept the king side files closed. After exchanging a pair of rooks the white queen moved forward, evals came down. Leela captured two pawns, Stockfish countered by attacking the white king and reducing to a QB vs QB position. Leela pushed a passer forward, Stockfish gave its bishop and ended the game in a perpetual check. In game 100 Stockfish as white gave a pawn with an open file in the center. This time both engines castled short, evals came slowly down. The pawns stabilized, after some shuffling Stockfish regained the pawn and evals were close to 0. The engines reduced to a RB vs RB position, Stockfish took the bishop and Leela preferred a perpetual check draw over retaking the bishop.

 

Season 21 superfinal games 81-90

After 90 games Stockfish leads 15-6 with 69 draws. For the first time in the superfinal there were 3 game pairs which were biased in favor of black. Stockfish won two game pairs, its lead is now 9 points. Leela probably missed a win in one game. Leela's chances of catching up are purely theoretical with 10 more games to play.

In game 81 there was only one pawn trade after the start, the center was blocked and there was one open file on the queen side. Stockfish moved a rook forward on the king side, its king walked there without castling. Evals came down and the engines started to shuffle on move 25. There were no weak spots to attack, the game was adjudicated on move 59. Game 82 started similarly, this time Leela moved its queen forward on the queen side and grabbed a pawn. Stockfish trapped the queen and eventually Leela gave the queen for a bishop and a rook. Evals were close to 0, the engines reduced to a Q vs RB ending and the game was adjudicated after the pawn captured stopped.

Games 83-84 started with a King's Gambit Accepted, Kieseritzky gambit Berlin defense. In game 83 there was only one pawn exchange after the start. Leela diverged from the known line, after the pawns stabilized Leela castled long. Stockfish gave a knight for two pawns and opened the queen side. The engines played out a long PV agreement, evals came down and the game reached a RRN vs Q imbalance on move 30. Stockfish was 4 pawns up with 3 connected passers on the king side, but Leela used its pieces to block the black passers and the game was adjudicated early on move 38. In game 84 there were more minor piece exchanges after the start and Stockifsh castled short. Stockfish opened the queen side and moved a rook forward. The engines exchanged a pair of rooks and the white queen moved forward. The engines started to shuffle and evals came slowly down. There were a few pawn moves and piece exchanges, on move 71 the game reached a RB vs RB position. Leela wouldn't lower its eval, the game was finally adjudicated on move 112.

Games 85-86 started in the English symmetrical variation, a line where black gives a knight for two pawns, creating connected passers on the queen side, while white offers a rook. In both games black took the rook. In game 85 Stockfish walked its king to the king side and pushed the passers on the queen side. Leela pushed pawns on the king side, it thought long on a few moves but couldn't find a way out, evals kept increasing. One black passer reached the 3rd rank, Leela used pieces to block. 

Leela opened the king side with its pawns, but it didn't have the strength for an attack on the black king. Stockfish gave back a rook for a knight and created a 3rd passer on the queen side, then pushed it all the way to the 2nd rank.

Leela could only defend, Stockfish was on its way to win but it was still far. The black queen came forward, then Stockfish gave a rook for two pawns and removed any danger to its king. Stockfish attacked the black king with its queen and bishop, Leela managed to capture two passers on the queen side but Stockfish used checks to capture almost all the white pieces, with mate following. Incredibly, the black knight on g8 never moved in the game.

In game 86 the black queen came forward and Leela traded it for a bishop and knight. Stockfish gave a rook for a bishop and captured one black passer on the queen side, evals started to come down. The engines reduced to a QB vs RRN position on move 28 and Stockfish captured the remaining passers, clearing all pawns on the queen side. After a few pawns trades the engines started to shuffle, Leela wouldn't lower its eval enough for 5 straight moves and the game was adjudicated only on move 93. Stockfish wins the game pair, it leads 14-6.

Games 87-88 started with a Sicilian dragon, Yugoslav attack. In both games the engines castled in opposite directions. In game 87 Stockfish pushed pawns and opened the queen side, Leela pushed a pawn to h6. Evals kept increasing as Leela prepared to open the king side. On move 27 Leela pushed f4 and Stockfish took it with a pawn, Leela naturally took back with its queen and immediately Stockfish's eval dropped. Leela thought for 13 minutes and its eval dropped as well. I don't really understand what Leela missed, the engines continued with a long PV agreement and exchanged most pieces. On move 39 the game reached a RB vs RB position, evals were close to 0 and the game was adjudicated. This seems like a missed win by Leela.

In game 88 Leela pushed pawns on the queen side and Stockfish captured one. Stockfish did not push pawns on the king side, it concentrated its pieces on the queen side. Evals increased slowly, Leela threatened the b2 pawn with all its major pieces but Stockfish's defense was sufficient. Stockfish turned to the king side, it gave back the pawn and opened a file on move 34. The white queen came forward and exposed the black king, Leela tried to exchange pieces but Stockfish was determined to avoid this.

Stockfish had a clear advantage in the open position, its king was safe in the corner while the black king was exposed and in danger. After exchanging a pair of rooks Stockfish attacked with its queen and rook, Leela was under constant threat of mate. On move 62 the remaining rooks were exchanged, evals were over 11 by then.

Stockfish quickly captured the two black pawns, Leela chose to give up its queen and be mated, rather than to delay the loss or reach a tablebase position. Stockfish wins the game pair, it leads 15-6. 

In game 89 there were no exchanges after the start and evals came down. On move 19 the engines opened a file on the king side, then Stockfish captured a pawn on the queen side. After some shuffling the engines opened the queen side and Leela regained the pawn. Leela had a passer on the queen side but evals were close to 0. Leela captured a pawn on the king side and created a second passer, Stockfish gave a rook for a knight and pawn to create two central passers, then attacked the white king. Leela offered the exchange back, Stockfish preferred to capture the king side passer. The pawns stopped moving and the game was adjudicated.  In game 90 there was one pawn trade after the start without opening a file. The engines developed behind the pawn lines and exchanged minor pieces. On move 32 there were no  knights on the board, Stockfish's eval was over 1 but all it could do was shuffle. A few pawn moves extended the game, adjudication came finally on move 114.

Season 21 superfinal games 71-80

After 80 games Stockfish leads 13-6 with 61 draws. Leela won one game pair, reducing Stockfish's lead a little. However the lead is still very significant with only 10 more game pairs to play in the superfinal.

In game 71 Stockfish's eval was around 1 from the start. After the engines completed their development Stockfish opened a file on the queen side and moved a rook forward. Leela took over the open file and its eval started to increase. Stockfish grabbed a pawn on move 24, Leela thought that was a mistake. It thought for 8 minutes, its move surprised Stockfish and its eval jumped over 3. Leela moved a rook to the back rank, and the black forward rook was trapped.

Stockfish tried to counter attack with its queen on the king side while Leela doubled rooks on the back rank. Stockfish managed to exchange queens, capture another pawn and break its rook out of the trap. However, Leela captured the black bishop and reduced to a RB vs R position on move 38.

The engines traded pawns, Leela was down to its last pawn and it made sure it was protected by its king. Stockfish tried to avoid exchanges and a tablebase position, Leela pushed its pawn slowly. When the pawn reached the 7th rank Stockfish had no choice but to take and accept the loss.

In game 72 there were no exchanges for a while after the start. From move 15 the engines played out a long PV agreement, the queen side opened, a pair of knights was exchanged and Stockfish went a pawn up. Gradually more pieces were exchanged, on move 41 only RRN vs RRN remained. The engines shuffled for 30 moves without changing evals, then they reduced to rook ending. Stockfish was still a pawn up but that was only good for a draw, the game was adjudicated on move 109. Leela wins the game pair, Stockfish leads 13-6.

Games 73-74 started in the Neo-Gruenfeld defense with the engines castling in opposite directions. In both games the engines followed a known line until move 15, where white has a central passer. In game 73 the engines played out a long PV agreement until move 24, exchanging a few minor pieces. Evals came down as the engines continued to exchange pieces, reaching a QRR vs QRR position on move 30. The engines exchanged a pair of rooks and Leela went a pawn up, but evals were close to 0. Leela gave a queen for a rook and pushed its passer to the 7th rank. Stockfish ended the game in a perpetual check draw. In game 74 the engines continued differently but still with a long PV agreement, exchanging a few minor pieces and opening a file in the center. Leela gave its queen for two rooks, Stockfish pushed the passer to the 6th rank but there it was captured. The engines reduced to a QB vs RRN position, evals came down and the game was adjudicated when the pawns stopped moving.

Games 75-76 started with a wild 20-ply book in the Vienna Steinitz gambit, white was a knight and pawn up, the white king was exposed on e2, the black king was hiding behind a white pawn on the queen side. The games repeated 12 plys, white gave back a knight, the engines exchanged queens and the white king came forward. Game 75 continued with a long PV agreement, the engines reduced to a double rook ending with Leela a pawn up on move 28. Evals came down, Stockfish regained the pawn and exchanged a pair of rooks. The game was adjudicated when the pawns stopped moving. In game 76 the engines exchanged a pair of rooks, Stockfish was up a pawn and tried to keep two passers on the queen side. The engines reduced to a RBN vs RBB position on move 28 and evals came down. Stockfish couldn't push its passers forward, eventually the rooks were exchanged and evals were close to 0. The engines continued to exchange pieces and pawns until reaching a drawn bishop ending.

Games 77-78 started with a 20-ply book in the French MacCutcheon, Dr Olland variation, black was a pawn up and white was ahead in development. In game 77 Leela gave away two more pawns, then in a PV agreement the engines exchanged queens and Leela captured two pawns back. The black king came forward, Leela castled late, evals came slowly down. The black queen side rook was trapped in the corner, Stockfish found a way out for it and in a series of exchanges the engines reduced to a RB vs RB position. Leela was up a pawn but it was only good for a draw. Game 78 repeated almost excactly, on move 26 the position was still the same as in the previous game. Stockfish equalized material, the pieces stayed on the board longer. The game reached a RBN vs RBN position on move 35 and Stockfish went a pawn up. Stockfish had a passer on the king side, however both evals were close to 0 and the game was adjudicated.

Games 79-80 started with a 26-ply book in the Ruy Lopez closed, Chigorin defense, without any exchanges. In game 79 the engines opened the king side, Leela exchanged minor pieces and pawns and the black king was left with one supporting pawn. Leela attacked with its queen moving forward, then a series of exchanges left a RN vs RN position. Leela had a passer on the king side but evals were low. After exchanging knights Leela went up a pawn, its eval came down slowly and the game was adjudicated only on move 100. In game 80 the engines opened the queen side and exchanged a few pieces there. Stockfish moved its queen forward but Leela blocked the entry. Evals came down and the game was adjudicated with most pieces on the board.

Season 21 superfinal games 61-70

After 70 games Stockfish leads 13-5 with 52 draws. Leela won a game pair, but then Stockfish replied with 4 straight game pair wins. Leela clearly blundered in one game, and in another game it realized it was in trouble long after Stockfish's Eval increased. Stockfish's lead is now 8 wins, it is very hard to imagine that Leela can close this gap in the remaining 15 game pairs.

In game 61 Leela went up a pawn, though it was left without pawns in the center. The engines played out a PV agreement, Stockfish castled and Leela kept its king in the center. Evals increased as many pieces were exchanged in the center, including the queens. Only rooks and bishops remained on move 22, Stockfish had a passer in the center while Leela had a pawn majority on the queen side.

 

Evals did not change for a while, the engines traded pawns on the queen side until Leela had one passer left there. Stockfish gave a rook for a bishop and pushed its passer to the 6th rank. Leela managed to capture the passer, and had to give back a rook for a bishop.  On move 41 Leela was two pawns up in a RB vs RB position.

The endgame was very long, Stockfish avoided exchanging pieces and Leela slowly pushed its passer forward. On move 77 Leela captured the black bishop, there was no way to stop the queening and mate followed.

In game 62 both engines castled short, the center remained blocked and the engines opened a file on the queen side. Stockfish had a space advantage and eval over 1.5, but evals did not change a lot. The queen side became blocked, the engines opened a file on the king side. On move 43 only RBN vs RBN remained, the engines mostly shuffled. Stockfish's eval came down, it gave a pawn but couldn't create an attack. The game was adjudicated on move 96. Leela wins the game pair, Stockfish leads 9-5.

In game 63 Leela pushed a pawn to h6, then gave a knight for 3 pawns on the queen side, creating 3 connected passers. Leela castled long, Stockfish kept its king in the center. The game reached a RR vs RRN position on move 29, the king side pawns locked and evals came down. After exchanging a pair of rooks the white king came forward. Stockfish captured a few pawns while Leela created a passer on the king side and pushed it to the 7th rank. Stockfish lost its knight to captured the white pawns on the queen side, the resulting rook ending was a draw.

In game 64 the engines castled in opposite directions, Stockfish pushed pawns on the king side, gave a pawn and opened files near the black king. Leela pushed pawns on the queen side and didn't seem to be worried about its king's safety. Stockfish gave a knight and its eval jumped over 2, then it gave more material and was a rook down. Leela's eval was still low though its king looked very vulnerable.

For a while Stockfish had second thoughts, its eval dropped to 1 and it thought Leela may be all right if it gave its queen for a rook. However Leela had other ideas and Stockfish's eval jumped back up. Stockfish captured a rook and Leela tried to expose the white king with its pawns. On move 37 Leela finally acknowledged it was in trouble and its eval jumped over 5. The white king hid behind doubled black pawns, and a series of exchanged led to a BB vs R ending.

Material seemed balanced but the black king was trapped and the rook could do very little on its own. Stockfish pushed its passer forward and queened, the game ended in mate. Stockfish wins the game pair, it leads 10-5.

In game 65 the engines castled in opposite directions. Stockfish's eval came down quickly, Leela tried to attack on the king side and at one point its eval went over 1, but then quickly came down as well. Leela gave a knight and 3 pawns but it had a passer on the 7th rank. The black king blocked the passer and appeared to be in danger. Stockfish gave the knight back, a quick counter attack allowed it to force a 3-fold repetition draw.

In game 66 there was a similar setup, Stockfish was more patient with its king side attack. Material stayed equal, Leela pushed pawns on the queen side and one reached a3. Stockfish finally opened the king side and on move 37 the pawns there were all gone and the black king was exposed. However, evals were low and the game seemed to be heading for a draw. On move 43 Stockfish's eval jumped over 5 without warning, Leela apparently blundered ?! Stockfish created a central passer and Leela captured a knight, but Leela totally overlooked 44 Rh8+ :

Leela can't play Nxh8 because of d7+ (if c5 then d8=Q+ is check). Leela's eval jumped to 33 (!) after 37 minutes thinking (!!), it had to play Kg7, but then 45. Qc3+ is almost mate. After Re5, 46 Qxe5 Nxe5 47 Rh7+ Leela lost its queen, and the aftermath was a RB vs BN position with white two pawns up and a passer on d6. Stockfish gave the rook for the knight and reduced to a winning bishops ending. Stockfish wins the game pair, it leads 11-5.

In game 67 the engines played out a long PV agreement and opened the queen side. Leela went up a pawn and created a passer on the queen side, but Stockfish's eval came down. The engines continued to exchange pieces and on move 40 the game reached a B vs N ending. Leela wouldn't lower its eval and the engines shuffled, the game was finally adjudicated on move 97.

In game 68 there were only a few exchanges after the start and the queen side stayed closed. The engines started to shuffle on move 23, with pawn moves extending the game. On move 128 (!) Stockfish traded a pawn on the king side, evals were low and Leela's eval even turned slightly negative. Stockfish's eval was not low enough and the shuffling continued. Stockfish's eval started to increase slowly from move 152, it went over 1 and stayed there for a while. The shuffle continued but Stockfish had a long term plan. On move 169 Leela exchanged bishops on the king side, Stockfish moved its pieces there and doubled rooks on the h file. Stockfish's eval jumped over 2 and continued to increase, it waited for the right moment to break the pawn wall with a sacrifice. On move 192, with its eval over 8, Stockfish started the attack.

Stockfish gave two rooks on h6 for a knight, but Leela had to give its queen to avoid mate. The game reached a Q vs RR position, with a passer on g6. Leela had to defend against a back rank mate threat, Stockfish gave a pawn to create a second passer on e6. Leela was nearly paralyzed, the white king came forward and Stockfish started to see mate.

There was no way to prevent Qf7+, reducing to a won king and pawns position. Stockfish wins the game pair, it leads 12-5. Note that the engines had less than a minute on the clock and were in blitz mode for the last 100 moves of the game.

In game 69 there were a few exchanges after the start, the engines concentrated mainly on the queen side. A series of exchanges that started on move 24 cleared all pawns on the queen side, queens were off and Leela was a pawn up. Stockfish's eval gradually came down, the exchanges continued and on move 46 the game reached a knight ending. Leela wouldn't lower its eval, the engines shuffled and the game was adjudicated only on move 82.

In game 70 the beginning was similar, and again the engines concentrated on the queen side. The black queen moved forward and Stockfish's eval went over 1.5 and kept increasing. Leela thought it was perfectly safe, a series of exchanges reduced to a RRB vs RRB position on move 25, Stockfish's eval was over 2.5 already.

Stockfish gave the e pawn and pushed the d pawn to d6. Stockfish's 29th move caught Leela by surprise, it thought almost 9 minutes and its eval jumped over 12. Leela gave its bishop and captured the white passer. Stockfish exchanged a pair of rooks and reduced to a RB vs R position.

Leela was two pawns up with two passers on the queen side, Stockfish kept the black king away and moved its king to block the passers. It then used its piece advantage and the exposed black king to gradually capture black pawns until there were none left. The game ended in a tablebase win. Stockfish wins the game pair, it leads 13-5.

Season 21 superfinal games 51-60

After 60 games Stockfish leads 9-4 with 47 draws. Stockfish added two game pair wins, increasing its lead to 5. Leela needs wins to try to catch up, this is looking more and more like another Stockfish superfinal win.

In games 51-52 white castled long while black kept its king in the center and pushed pawns on the king side. In game 51 the engines played a very long PV agreement, starting from Stockfish giving a rook for a knight. Stockfish castled short and fortified the king side with its bishops. On move 37 the game reached a RR vs RB position, still in PV agreement and with evals under 0.5. By move 56 both engines were down to their last pawn. Both pawns advanced slowly, both were eventually one square away from promotion. Evals were low enough for adjudication on move 94 after the pawns stopped moving.

In game 52 again the engines played out a long PV agreement but this time material was equal, Stockfish's eval increased steadily.  After Leela castled there was a series of exchanges, the engines reduced to a RBB vs RBB position and Stockfish went a pawn up.

Stockfish concentrated on the queen side where it had a pawn majority. It gave a pawn to disconnect the black pawns and create a passer. Leela couldn't protect both its pawns there and Stockfish captured one. After exchanging a pair of bishops Stockfish connected a second passer on the queen side, evals were over 5.

The ending was slow, Leela did all it could to delay the white pawns on the queen side. After 30 moves Stockfish finally promoted a pawn and Leela had to give its rook to capture it. There were no white pawns left but the material was sufficient for a win. Stockfish wins the game pair, it leads 8-4.

Games 53-54 started with a 6-ply book in the Robasch defense with black offering a pawn. In both games white took the pawn, but then the games diverged from the usual line and black didn't take back immediately. In game 53 the engines continued to develop with a few exchanges and evals came down. The queens were exchanged early, Leela kept its pawn advantage but Stockfish trapped a white bishop. After a series of exchanges only RN vs RB remained, evals were close to 0 and the game was adjudicated when the pawns stopped moving. In game 54 there were a few exchanges after the start and the queens stayed on the board. Evals came down as the engines gradually exchanged pieces and pawns, the game was adjudicated in a QRN vs QRN position still with white a pawn up.

Games 55-56 started with another side-line variation in the Robasch defense. In game 55 Stockfish's eval was over 1 from the start. After Leela castled long the engines played out a long PV agreement. Stockfish gave a bishop for a pawn and castled short, then the material was equalized and the game reached a RRB vs RRB position on move 22. Stockfish's eval came down and the engines exchanged bishops. The engines shuffled and captured pawns until there were only two white pawns left on the king side. Both engines agreed this was a draw, though I was not aware of a double rook ending two pawns up (connected passers at that) that was a draw. The game was adjudicated when the pawns stopped moving. In game 56 both engines casled short. The engines again played out a long PV agreement, they exchanged pieces including queens and opened the queen side. Stockfish gave a pawn and then exchanged R for BN, reducing to a RBN vs RR position on move 37. After exchanging a pair of rooks the engines shuffled until Stockfish lowered its eval enough for the draw rule.

Games 57-58 started with a Caro Kann variation that both engines thought were completely drawn. In both games the black queen came forward and captured the b2 pawn and the rook in the corner, white captured a bishop and trapped the black queen. In game 57 Stockfish gave its queen for two minor pieces, the game reduced to a QR vs RRN position on move 18. Stockfish pushed a passer on the queen side, Leela blocked with its rook, the game ended early by a 3-fold repetition. In game 58 Leela gave its queen for RB, the game reduced to a QB vs RRN position on move 25. Evals were low, Leela surrounded its king with pieces, the game was adjudicated when the pawns stopped moving.

In game 59 the center was blocked, the engines formed long pawn lines without exchanges. All bishops were exchanged and the white king moved to the king side without castling. There was one pawn trade on the queen side, files were still closed and the engines shuffled for a while. Leela tried to attack from the king side, Stockfish captured a pawn and created a passer on the queen side, its eval coming down. Stockfish gave a knight for a pawn and reduced to a QNN vs QN position. Leela's queen blocked the black pawns on the queen side, Stockfish exchanged a pair of knights and its queen gave checks to the exposed white king. The game was adjudicated with the PV predicting a drawn queen ending.

The start of game 60 was a little different but it transposed back to the previous game, then followed the same move sequence until move 23 with no bishops and one pawn trade on the queen side. After shuffling for 20 moves Stockfish pushed the g pawn, Leela's king was still uncastled and the king side stayed closed. Stockfish's eval jumped over 3 though it seemed to continued shuffling its rooks, it doubled rooks on the c file and pushed a pawn there.

A series of exchanges opened the queen side and Leela quickly castled. Stockfish went two pawns up and the game reduced to a rook ending. Stockfish had doubled pawns on the king side, so perhaps less than a full two pawn advantage, but Stockfish saw the win.

Both engines pushed pawns forward, Leela couldn't hold on to its pawn with its rook in front. It refused to take a white pawn, trying to avoid a 6-man position, but eventually gave up. Stockfish wins the game pair, it leads 9-4.