Season 19 superfinal games 91-100

Stockfish wins the season 19 superfinal. The final result is 18-9 with 73 draws. In the last 10 games Stockfish increased its lead by two game pairs.

The superfinal started with relatively a few decisive game pairs, after 50 games Stockfish led 5-4 and only 3 game pairs were decisive. In the second half of the match the draw rate dropped to 64% and the score was 13-5. I think Jeroen mentioned in the chat that the opening bias was designed to increase as the match progressed. Still it was unexpected that Leela did not win any game pair in the second half while Stockfish won 8.

This season Stockfish used NNUE, with a neural net for evaluation (on CPU I think? not sure). The NN revolution that started with AlphaZero, and Leela's first participation in TCEC season 12 two and a half years ago, appears to be complete. This season both TCEC superfinalists, indeed the top 4 engines in the premier league, all used neural nets for evaluation. Other engines switched to NNUE and there may be more new NN engines being developed. How long until there are no "classical" evaluation engines playing in the premier league?

In the lower leagues we saw the rise of SlowChess, a new non-NN engine that started from qualification and reached league 1. Igel started in league 3, then transformed to Igel NN and this boosted it to league 1 as well. In the premier league Stockfish and Leela led from early on and most of the attention was the race at the bottom of the league. Four engines battled against relegation, including former champion Komodo. In the last DRR Komodo moved up with a few rare wins, Ethereal dropped to last while Fire and ScorpioNN were tied in the last round. In the end it was Fire that relegated and ScorpioNN survived.

I suppose the added NN improved Stockfish's opening abilities, this was always the strong point for Leela. Looking at some of the games of the superfinal suggests that Stockfish NNUE and Leela made similar choices in the opening, much more than before. In my statistics report you can see that the distribution of equal moves after book is much more flat than ever before in TCEC, so the game pairs repeated more moves than usual. In games 21-22 with a 2-ply book the games diverged after 21 plys. Games 25-26 also had a 2-ply book, the games diverged after 25 plys ignoring an early move transposition. The engines are still not the same, in games 45-46 there was a 2-ply game and the games diverged after only 6 plys.

On a personal note, in season 19 the blog reached 100K all time views. I enjoy looking at the geographic distribution of readers, spread all over the world. This is not something I imagined when I started it 5 years ago. Thank you for reading, I welcome comments and corrections.

The corona virus is still with us, this week there was a new record of ~500K people testing positive in a day. 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.

See you next season,

Go TCEC!!

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In game 91 Leela developed its rook through the h file and didn't castle, while Stockfish castled long. There were only a few exchanges after the start and the engines locked pawns in the center and queen side. On move 30 Leela opened a file on the king side and evals increased over 1.5. The engines exchanged pieces through the gap until the game reached a RN vs RB position. Leela's eval was over 2 but it couldn't break through the black pawn wall. The engines shuffled and Leela moved its f pawn reluctantly while the evals came slowly down. On move 103 Stockfish took the f pawn and evals dropped close to 0, after a few pawn exchanges the game was adjudicated. Did Leela miss a win?

In game 92 Stockfish castled and Leela kept its king in the center. Leela pushed a pawn on the queen side, a pawn exchange opened a way for a white rook to move forward. Stockfish thought that Leela's move 21 was a mistake, it should have tried to castle its king. When it didn't Stockfish's eval jumped, it sacrificed a knight and forced the black king to move.

Leela's eval reacted 5 moves too late. Stockfish doubled rooks and attacked the a pawn, after a series of exchanges the game reduced to a Q vs QB position and Stockfish had 5 extra pawns for the piece.

Leela had too many pawns to worry about, and its king had no protection except the bishop. Stockfish let the 2 pawns on the queen side be captured while it moved its king forward, finding protection from the black queen that was behind the pawn line.The e pawn marched forward and Leela could not stop it, it lost its queen and the game. Stockfish wins the game pair and its lead increases to +8.

In game 93 there were no exchanges after the start, Stockfish formed a pawn line across the board. After most of the minor pieces were exchanged the engines shuffled for a while, then Leela opened a file on the queen side. The engines exchanged all rooks through the gap in the wall and the game reached a QB vs QB position on move 28. Stockfish gave a pawn and moved its queen forward where it could give checks. Evals were close to 0 and the draw rule stopped the game quickly.

In game 94 Leela formed a pawn line as well but it was less stable than in the previous game. Stockfish exchanged a pair of pawns on move 16 and opened a gap in the line, after a series of exchanges the position opened. Stockfish was a pawn up with a central passer though its pawn structure looked awful. Both kings were vulnerable on the open g file. Stockfish thought it was better with an eval over 2.

Leela placed a rook on the g file first. Stockfish exchanged pawns and removed the black pawn on f5, making its f pawn a passer. Leela blocked the second passer with its rook and Stockfish took over the g file. By the time Leela captured the f pawn Stockfish lined up all 3 major pieces on the g file.

Leela needed all available pieces to defend its king, and one rook was too far to help. Stockfish moved its queen forward and pushed the passer, Leela could not stop it. Stockfish got a bishop for the passer, mate was coming when the game was adjudicated. Stockfish wins another game pair, increasing its lead to +9.

Games 95-96 started with a 20-ply book in the Vienna opening, where the black king moved without castling and white captured a rook with a knight, which is trapped in the corner. In game 95 Stockfish captured the knight and Leela castled its king. Stockfish pushed 4 pawns on the king side, it gave one away but managed to trap and capture a knight. Stockfish's eval was 0, it opened the king side and attacked the white king. After a series of exchanges only RR vs RBN remained on move 38. The engines continued to exchange pieces and pawns, the game ended in a tablebase draw. Game 96 repeated the same moves for 30 plys, except for a few early transpositions, resulting in a R vs NN imbalance and advanced black pawns on the king side. Leela opened the king side and evals were close to 0. The engines reduced to a rook ending with Stockfish a pawn up, the pawns did not move and the game was quickly adjudicated.

Games 97-98 started with a 26-ply book, a high level line in the King's Indian defense, orthodox variation. The center was locked and there were no early exchanges. In game 97 the engines exchanged a pair of pawns and a pair of knights on the queen side, but made no attempt to attack. Stockfish opened a file on the king side and the engines exchanged a pair of rooks. Evals were close to 0, the pawns did not move and the draw rule ended the game quickly. In game 98 Stockfish attacked on the queen side, it captured a pawn and its eval jumped over 1.5. Leela pushed pawns on the king side and gave another pawn, Stockfish's eval dropped back to 0. Leela sacrificed a knight and opened the king side, a queen and a knight were sufficient to force a perpetual check draw.

In game 99 there were a few minor piece exchanges after the start, Stockfish went a pawn up and its eval dropped to 0. The engines started to shuffle on move 25, Stockfish was content in defending its fortress and Leela made no attempt to attack it. There was one pawn move until the game was adjudicated on move 92. In game 100 Stockfish castled long, Leela gave a pawn and tried to attack on the queen side. Stockfish was not worried, its eval dropped to 0 as it exchanged a pair of rooks and created a central passer. Leela was busy blocking the passer, its eval was low enough for the game to end quickly by the draw rule.

Season 19 superfinal statistics

A summary statistics table of previous stages and seasons. 

Draw rate, wins

Final draw rate was 73%.

Game termination

The three most common game termination causes were:

62% - TCEC draw rule
26% - TCEC win rule
8% - SyzygyTB

There were no crashes in the stage.

Moves per game

 

Median= 55.5
Average= 69.1

There were 13 games longer than 100 moves, the longest was 213 moves (Stockfish - Leela, game 10, draw).

Time per game (hours)

 

 
Median= 3:51
Average= 3:45

Openings

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

 

The engines had almost no freedom to choose the opening variant, all games repeated the same ECO twice, 96% of the game pairs repeated the same opening variant.

Reverse pairs, wins

Reverse pairs, same moves  

Pairs of reverse games diverged much more slowly than usual, only 14% diverged immediately out of book, 42% of the pairs diverged at most after 1 move. The longest repeated sequence of moves was 21 plys (Leela - Stockfish games 21 and 22, Ruy Lopez Berlin defense - book was 2-ply 1.e4 e5, two draws)  

 

Season 19 superfinal games 81-90

After 90 games Stockfish leads 16-9 with 65 draws. Stockfish won another game pair and its lead is now +7. Leela's chance of catching up is only theoretical with 10 games left to play.

Games 81-82 started with a 21-ply book in the King's Indian Samisch variation, popular in games from the 90's. In game 81 there were no exchanges after the start, Leela castled long and the engines played behind their pawn lines. Stockfish opened the queen side, then gave a rook for a bishop and its eval dropped to 0. The engines cleared the queen side pawns and reduced to a QRR vs QRB position. Leela moved its pieces forward and Stockfish ended the game with perpetual check. Game 82 started similarly, Stockfish castled long and there were only a few exchanges. This time the engines exchanged a pair of pawns on the king side, Leela blocked the entry and the engines shuffled for a while. On move 34 Stockfish gave a rook for a bishop and created an advanced passer on the queen side . Evals were close to 0 and without pawn moves the game was quickly adjudicated, most pieces still on the board.

Games 83-84 started with a 20-ply book in the Sicilian Taimanov variation, with the engines castled in opposite directions. There were many early exchanges in game 83, the game reached a RBB vs RBB position on move 19. After a few pawn moves the engines started to shuffle, on move 53 the rooks were exchanged. After almost 50 more moves Leela gave a pawn and used a pawn majority on the queen side to create a passer. Another 50 moves went by, Leela realized it had nothing after another pair of pawns were exchanged and it lowered its eval. The game was finally adjudicated on move 161.

In game 84 Leela avoided exchanging knights immediately, it prefered to trade a knight for a bishop. Stockfish's eval jumped over 2, the black king faced advanced pawns and many white pieces while the black pieces were mostly on the queen side.

Leela had to exchanged its DS bishop with a knight, this got a white pawn to f6. Stockfish had several options to attack the black king, and the g6 pawn was a crucial defender. Leela had a counter threat against the white king but Stockfish protected its b2 pawn and continued the pressure on the king side. On move 28 Stockfish was willing to give a rook to get the g6 pawn out of the way.

Leela refused to take as it knew this would lead to a quick loss of material or mate on either g7 or h7. Instead there was a quick series of exchanges, queens were off and Stockfish traded its f6 pawn with the black c5 pawn. Material was equal in a RRB vs RRB position but Stockfish's queen side pawn majority was deadly. Leela's pawns on the king side could never be quick enough, the white pawns started to march and Leela had to lose pieces to stop them. Stockfish wins the game pair, its lead increases to +7.

Games 85-86 started with the QGD Chigorin defense with black a pawn up, and in both games black played a very rare move of retreating a knight to b8 immediately out of book. In game 85 Leela regained the pawn, there were almost no exchanges as the engines formed long pawn lines. On move 32 Stockfish completed a line across the board and the engines started to shuffle. On move 90 the engines started to exchange pawns and opened the position, Leela went a pawn up and created a queen side passer and Stockfish had a passer on the king side. On move 107 the game reached a RB vs RN position, Leela gave the bishop and pushed its passer to the 7th rank. However Stockfish gave checks and the game was adjudicated before it lost its knight and stopped the passer. Game 86 started similarly, Stockfish regained the pawn and the engines developed their pieces without exchanges. Stockfish pushed a pawn to a6, then the engines opened the queen side and exchanged a pair of rooks. After some shuffling the evals came down, a series of exchanges reduced to a RB vs BNN position. The engines cleared the remaining queen side pawns and the game reached a R vs B ending. It took a while for Stockfish to lower its eval enough for the draw rule to stop the game on move 93.

Games 87-88 started with a 26-ply book in the Ruy Lopez Flohr system. The white 13th move in book was rare, but in both games the engines transposed back to the main line for a few moves. In game 87 the engines continued without exchanges until move 29, Stockfish pushed pawns on the queen side and created a passer. Stockfish gave a rook for a bishop and a series of exchanges cleared all the white pawns on the queen side. Evals came down as the exchanges continued more slowly, on move 62 the game reached a R vs N ending. Leela managed to capture the black passer, the game was adjudicated in a 7-man draw. In game 88 there were no exchanges until move 29 as well, though the development was not the same. Leela had a pawn majority on the queen side but it didn't push the pawns too much forward. Instead Leela tried to create some pressure on the king side with its queen and knight. Evals were close to 0 when the engines started to exchange pieces and the position opened up. Stockfish had a back rank threat, and when Leela captured a rook Stockfish ended the game in a perpetual check repetition.

In game 89 Stockfish captured an early pawn but its eval was over 3 very quickly. Leela regained the pawn and developed all its pieces, while Stockfish was slow developing its queen side. Leela started attacking on the king side and Stockfish traded RN for Q on move 21.

The white queen was very strong in the open board and Stockfish had to deal with multiple threats. The black defense crumbled quickly, on move 34 Leela captured a rook for a knight.

Leela captured the bishop and Stockfish saw the mate coming when the game was adjudicated.

The start of game 90 was more peaceful, the engines developed their pieces without exchanges. Only Stockfish's increasing eval gave a hint that something was happening. The black pieces had only a small space to move, on move 19 Leela gave a pawn and tried to open the queen side. Stockfish's eval jumped over 3.

Stockfish pushed pawns in the center, it gave the e pawn and created a passer on the d file. The white DS bishop was en prise for 4 consecutive moves but Leela had more urgent things to do like protecting the f7 pawn. Eventually the engines exchanged their DS bishops, Leela went a pawn up and Stockfish pushed the passer to the 7th rank. In a series of exchanges the engines reduced to a QRB vs QRN position and Stockfish captured the black pawns on the queen side. Now Stockfish was a pawn up with connected passers.

Leela did not have a threat against the white king and it needed to keep the white pawns from queening. With a pawn on the 7th rank the engines exchanged rooks and Stockfish captured another pawn. The game was adjudicated before Stockfish won more material. There were two white wins in this opening, Stockfish continues to lead +7.

Season 19 superfinal games 71-80

After 80 games Stockfish leads 14-8 with 58 draws. Stockfish won 3 game pair wins and it doubles its lead to +6, with only 20 games remaining. It is quite incredible that Leela has not won a game pair since games 23-24, and hard to imagine that Leela can close the gap at this stage.

Games 71-72 started with the Haloween Gambit, with black a knight for a pawn up. In game 71 Leela pushed the pawns in the center to drive the black knights back, then opened a file in the center and the black king moved after check. Leela castled long, Stockfish captured a pawn with its queen and the engines exchanged queens. Stockfish gave the knight back but was two pawns up. Only rooks and bishops remained, evals were still negative but close to 0. The white pieces were more active and the black king was not safe, Stockfish was busy defending despite the material advantage. The engines started to repeat and shuffle and the game was adjudicated. In game 72 the black king didn't move right away, instead the engines exchanged queens early. Stockfish forked king and rook with its knight, leading to a R vs NN imbalance. The engines exchanged pieces and the game reached a RR vs RNN position on move 26. Evals were close to 0, the engines continued to exchange pawns and pieces, Stockfish gave a rook for a knight to create connected passers on the king side. The extra black knight and the white passers canceled out, the game ended in a tablebase draw.

In game 73 both engines castled short despite the fact the the g file was half open, so the white king was partially exposed and the black king could be attacked through the opening. Most action was on the queen side though, by move 18 Leela created a pawn majority there. The engines exchanged most minor pieces and Stockfish's eval dropped to 0. While Leela pushed pawns on the queen side Stockfish maneuvered its knight to h3 and a rook to the g file to trap the white king. Leela saw the problem and waited for a while. When it resumed the pawn march on the queen side Stockfish reduced to a queen ending. Leela had an unstoppable passer, but when it promoted (to a rook, because it didn't matter) Stockifsh had a perpetual check draw.

The g file stayed closed in game 74, both engines castled short and their kings appeared to be safe. There were almost no exchanges after the start, Stockfish pushed pawns on the king side. Leela had two bishops and a knight surrounding its king against a possible attack. On move 21 Stockfish exchanged a pair of pawns on the king side and opened the g file for its rook.

Stockfish's eval started to increase, Leela used the g pawn to remove the white pawn on f5, ans this fully opened the g file. The black pieces tried to cover all squares near the king, Stockfish gave a rook for a knight and took out a crucial defender. The black king was exposed, yet Leela's eval stayed below 1. On move 31 it thought for a long time. 

This was the realization moment for Leela, after almost 9 minutes its eval jumped to almost 5. Stockfish's rook joined the attack and the engines started to exchange pieces. The whole point of the attack was that after only NN vs RB remained Stockfish pushed a passer to c7 with the knight on e7 covering the promotion square. Leela was forced to give a rook to stop the pawn, Stockfish had an extra piece and two more pawns to complete the win. Stockfish wins the game pair, its lead is now +4.

Games 75-76 started with engines castling in opposite directions, the center blocked and no exchanges. In game 75 the engines opened the king side but only one pair of pawns was exchanged. After exchanging most minor pieces each engine placed a bishop to close a hole in the pawn line. Stockfish threatened the white king, this kept the white pieces busy defending.  The engines started to shuffle, it took Leela a long time to lower its eval for the draw rule.

All pawns stayed on the board in game 76, the engines exchanged most of the minor pieces and formed long pawns lines across the board. The engines shuffled for a while, then Leela doubled rooks on the h file and opened it. Stockfish blocked the entry and the engines started to shuffle. After 30 moves Stockfish's eval jumped over 1, it exchanged a pair of rooks and managed to take control of the open file. Stockfish's eval went down below 1 as the engines started to follow a long PV agreement, then it jumped over 2 again. Probably the limited thinking time caused the eval to be more unstable. Stockfish forced a queen exchange and only RN vs RB remained, still on the PV line.

Stockfish captured the g pawn and its threat on the f pawn forced the black rook to be passive. Leela moved its king back to support the f pawn but it couldn't stay since Stockfish threatened the queen side. Leela traded its f pawn for the white b pawn, this created a king side passer for Stockfish. Stockfish slowly pushed the passer to the 6th rank, Leela's eval started to increase. Stockfish opened the center with a pawn exchange, Leela equalized material and both engines had 2 pawns, all passers. However, evals clearly indicated that Stockfish was winning.

The knight on f6 denied crucial squares from the black rook, while covering the promotion square. Leela tried to block the g pawn with its bishop but Stockfish moved its rook to d7, again supported by the knight. Leela had to give the bishop to stop the pawn, the game was adjudicated 10 moves later. Stockfish wins the game pair, its lead increases to +5.

Games 77-78 started with a 24-ply book in the English symmetrical opening , 3 knights variation. Black was a pawn up and the white king could not castle after moving. In game 77 Stockfish castled early and Leela moved pieces to the king side. On move 18 Stockfish stopped to think for almost 23 minutes, it saw it was in trouble and its eval jumped close to 2. Leela was much stronger on the king side and on move 21 it threatened mate.

Stockfish blocked with the f pawn and then exchanged queens, the danger to the king was gone but Leela had connected passers in the center. Stockfish gave a knight to capture one of the passers, by then both evals were over 3.

Leela had a strong bishop pair, Stockfish exchanged the knight for one of the bishops and captured the e6 pawn. By then Leela had another passer in the center, and the extra piece was enough for a win.

In game 78 Leela did not castle at first, Stockfish created a passer in the center and regained the pawn. Stockfish chose to give away the passer to open a diagonal to the king side, Leela finally castled on move 28 but its king was still vulnerable. Leela exchanged a few pieces and its king moved to the corner, away from the open diagonals. Stockfish's eval increased over 2.

The evals didn't change for a while, Leela captured the two advanced white pawns on the king side while Stockfish cleared the queen side of pawns. Leela had to defend in a wide open position with many pieces, Stockfish is usually better at planning under these conditions. Stockfish's eval started to jump, Leela tried to block the entry points to the back ranks and it was still optimistic according to its eval.

Stockfish alternated its knight and bishop on f5, with the pieces supporting each other. On move 60 Stockfish managed to drive the black king back to the corner and pinned a knight on the back rank. Leela realized it was losing, the game reached a RB vs RN position and was adjudicated before Stockfish captured the knight. There were two white wins in this opening, Stockfish continued to lead +5.

In game 79 Stockfish did not castle its king, there were very few exchanges after the start. The engines opened the h file, the center pawns were locked and only the pawns on the queen side could move. The engines exchanged a pair of rooks and started to shuffle. Leela got nothing out of the open file on the king side, and after 40 moves it tried to open the center and queen side. Stockfish's eval came down, the engines gradually exchanged pieces and only QN vs QB remained on move 73. The game was adjudicated by the draw rule not long afterwards.

In game 80 there were no exchanges after the start, Leela pushed pawns on the queen side and delayed its castling. The engines openes the a file and Stockfish blocked it with a knight. The engines shuffled for a while and Leela castled on move 26. Leela gave a pawn on the queen side on move 39, after some more shuffling the engines started to exchange pawns and Stockfish's eval jumped over 2. On move 58 all pieces were still on the board, Stockfish was a pawn up with a central passer, and the white king looked completely exposed.

Stockfish started to move its king out of the king side. The engines started to exchange pieces and the game reached a QBB vs QBN position on move 71. Leela chased the white king all the way to the queen side, now the black king looked exposed.

Stockfish threatened mate with its queen and g pawn, Leela exchanged one bishop with a knight and eventually lost its bishop to stop the white passer. Stockfish then only had to force a queen exchange while keeping one pawn safe to win. Stockfish wins another game pair, increasing its lead to +6.

 

Season 19 superfinal games 61-70

After 70 games Stockfish leads 10-7 with 53 draws. There was one double white win and Stockfish's lead remained +3, now with only 30 games left to play in the match.

Games 61-62 started with a 6-ply book in the Czech Benoni Defense, and both games left known theory very quickly. In game Stockfish kept its king in the center and developed its king side rook through the h file. After exchanging a pair of rooks Leela started to push pawns on the king side. Stockfish's queen came forward on the queen side and captured two pawns, its eval came down to 0. Leela opened the king side with a bishop sacrifice, and two connected passers advanced towards the black king. Stockfish lost a knight for one of the passers, Leela threatened mate on the open file. However the black queen could attack the exposed white king and Leela had to stop its attack to avoid a perpetual check. The draw rule ended the game quickly. In game 62 both kings did not castle, there was one minor piece exchange after the start and all pawns remained on the board. On move 24 the engines started to exchange pawns, Stockfish went a pawn up and created a passer on the queen side. The engines shuffled for a while and evals started to come down. A few exchanges later the game reached a RBN vs RBN position, Leela captured two pawns and was a pawn up, Stockfish's passer was more advanced then the black pawns. Stockfish equalized material and pushed its passer to the 7th rank, Leela exchanged minors and pushed its own passer to the 2nd rank. Both passers could not advance further and the draw rule stopped the game.

In game 63 Leela moved its king early and could not castle, it developed the king side rook through the h file. Stockfish castled long despite an open file on the queen side. The engines started to shuffle on move 28, evals drifted down to 0, a few pawn moves and exchanges extended the shuffle to move 138. A series of exchanges opened the position, both queens move forward and both kings were exposed. The game ended in a check repetition. In game 64 both engines did not castle, Leela pushed a pawn to a3 and gave it away. The kings walked in opposite directions, Stockfish developed its king side rook through the h file. Shuffling began on move 18, on move 56 Stockfish gave the pawn back and the shuffle continued. Stockfish wouldn't lower its eval until the engines ran out of pawn moves, the game was adjudicated on move 187.

Games 65-66 started in the Benko Gambit, with white a pawn up and a queen side passer while its king is unable to castle after it moved. In both games the white king found safety on the g2 square. In game 65 Leela gave the pawn back, the engines traded pawns on the queen side and by move 31 they were all gone. Evals were close to 0, the engines traded NN for R and then the game was adjudicated. In game 66 Stockfish kept the pawn and pushed the passer to a5 where Leela blocked it. After some shuffling the engines reduced to a RRB vs RRN position and Leela regained the pawn. Evals came down and the game was adjudicated after the king side pawns stopped moving.

In game 67 Leela pushed pawns on the king side and castled long, Stockfish kept its king in the center. There were almost no exchanges and evals did not change a lot. Leela waited before opening the king side, it saw an opportunity and captured a pawn on the queen side. After a few minor piece exchanges evals started to increase, Stockfish moved its major pieces to the queen side and threatened the white king. Leela finally opened a file on the king side on move 36.

Leela considered how to proceed and the engines shuffled, Leela had to be careful to defend its queen side pawns. Leela couldn't decide which pawn to push, finally on move 56 it pushed the b pawn and created connected passers on the queen side. It took a while to get the rooks on the queen side and then Leela exchanged pieces until reaching a rook ending.

Leela was up only one pawn but its rook kept the black king away from the passers. The a pawn moved forward supported by the white king, the game was adjudicated with the pawn on a6.

In game 68 Stockfish pushed pawns on the king side and castled long as before, this time Leela castled short. Leela went up a pawn, it was not afraid of the white pieces on the king side and it even exchanged a pair of pawns there. Stockfish thought Leela made a mistake on move 26 and its eval jumped over 3.

Stockfish exchanged the defending knight on f5 and moved its queen to h6. Then it opened the king side with a rook sacrifice and forced a RR for Q trade. The black king was exposed and Stockfish controlled the dark squares.

The white passer was an additional threat that Leela had to deal with. Stockfish pushed it to the 7th rank but Leela captured it there after the knights were exchanged. Stockfish didn't seem to have an immediate threat, however it was confident it was winning and evals increased steadily.

The white queen danced on the board, Stockfish used mate threats to keep the black rooks on the back ranks. On move 62 Stockfish captured a pawn and created a passer on the queen side. Leela ran out of options, by the time the game was adjudicated Stockfish captured all the black pawns and one rook for a bishop. There were two white wins in this opening, Stockfish continues to lead by +3.

In game 69 Leela pushed pawns on the king side and opened the g file. After exchanging queens Leela had a bishop pair advantage. It pushed the black king to the corner, but with a rook and a bishop could only threaten a perpetual check. Stockfish's eval dropped to 0, Leela kept trying but could not improve its attack. Eventually Leela's eval came down as well, the engines started to exchange pieces until the game reached a drawn king and pawns ending. In game 70 Stockfish pushed pawns on the queen side and opened files there. By move 24 the queens were off the board, Stockfish was 2 pawns up and there was only one white pawn left on the queen side. Leela used its bishop pair to drive the white rooks away, it exchanged one bishop and captured one pawn back. The game reached a RRB vs RRB position on move 31, the engines mostly shuffled until Stockfish lowered its eval for the draw rule.

Season 19 superfinal games 51-60

After 60 games Stockfish leads 9-6 with 45 draws. There were 6 decisive games in the last 10, two double white wins and two stockfish wins. A lead of +3 is still small but compared to the results so far it may be significant with 40 games left in the match.

In both games 51-52 the engines castled in opposite directions. In game 51 there were many early exchanges. Leela's eval was constant around 1 while Stockfish's eval increased steadily. Leela pushed pawns on the king side and one pawn reached h6. The game reached a RRB vs RRB position on move 22, material was equal yet Stockfish's eval was over 2.5.

The action was on the queen side and the black king walked slowly to get there. Stockfish was caught in a web of pins in the center, and Leela threatened to play c4 and open a file in the center for its rooks. Stockfish chose to give a rook for a bishop to release some of the pressure.

Leela slowly shifted its rooks to the queen side and targeted the b pawn.Stockfish tried to keep files closed and it allowed the white a pawn to advance and become a passer. Then the white king came forward and Leela created a second passer in the center, the game was adjudicated a few moves later.

In game 52 Stockfish's eval jumped over 2 on move 14. It prepared its pieces for an attack on the king side after exchanging a defending bishop. Leela saw an opportunity to fork two white pieces with a pawn, Stockfish ignored this and went ahead with the attack.

It was quite incredible to see how long the d4 pawn could take a white piece, Stockfish played on and ignored it and Leela had more urgent things to do defending its king. Stockfish pushed the f pawn and used it to expose the black king. Leela had to avoid taking another free bishop because of a mate threat along the h file. A temporary rook sacrifice opened another file on the king side, Stockfish got the rook back and continued the attack. On move 32 Leela finally took a bishop with the d4 pawn, both the pawn and the bishop were static for more than 10 moves.

The second white rook joined the attack and Leela was forced to give its queen for a rook to avoid mate.The engines reduced to a Q vs RN position, Stockfish started to capture pawns and the game was adjudicated. Two white wins in this opening, very different games. Stockfish continues to lead by one win.

Stockfish opened the center early in game 53. The engines started to exchange pieces and Stockfish's eval came down. On move 34 the game reached a queen ending. After a while Leela went a pawn up, but Stockfish threatened either mate or perpetual check and this prevented Leela from capturing more pawns. Leela lowered its eval very slowly, the game was adjudicated on move 126.

In game 54 there were less exchanges after the start and the center remained closed. Stockfish thought Leela blundered in move 18 and its eval jumped over 1.5. It pushed a pawn forward and used a pin to exchange a pair of pawns and to create a passer in the center. This was also a restriction on the movement and influence of the black DSB.

Leela tried to exchange queens and Stockfish refused twice. Stockfish focused on the queen side, after exchanging a pair of rooks it captured a pawn. Leela's king walked back to the center to help with blocking the passer, evals increased and were over 4 on move 38.

Leela moved its queen forward in a desperate counter, Stockfish gave a knight for another pawn on the queen side. The black king was caught in a mating net and the game was adjudicated before Stockfish won more material. Stockfish wins the game pair and increases its lead to +2.

Games 55-56 started with the King's Gambit Declined, Norwalde variation. In game 55 Stockfish was a pawn up while Leela was far ahead in developing its pieces. Leela's eval remained under 1 with a very slow increase, Stockfish's eval jumped over 2 after Leela gave a second pawn on the queen side. Leela's eval jumped a few moves later, Stockfish captured a third pawn while Leela prepared for an attack on the black king.

The immediate danger was the b1-h7 diagonal. Stockfish captured the b1 bishop with its rook, Stockfish exchanged knights on f6 before taking back. The second white knight came forward and the black king was still vulnerable. Leela gave a rook for a bishop, when it seemed the attack was over Leela used a queen sacrifice and a knight fork to reduce to a RBN vs RB position.

Stockfish was 4 pawns up but all its pawns were isolated. Leela used its extra piece to pick the black pawns up one by one. After 30 moves Stockfish was down to its last pawn and the game was adjudicated.

In game 56 Stockfish regained the pawn right away, evals remained almost constant for a long time. Stockfish had a two bishops aimed at the black king, its LSB was on a strong central square. However Leela's defense looked solid and Stockfish didn't seem to have a plan. On move 24 Leela exchanged a pair of pawns on the queen side and its queen moved forward. Stockfish exchanged a pair of knights, its eval started to increase and was approaching 2.

Stockfish doubled rooks on the f file and the plan seemed to be attacking the f7 pawn. Stockfish could potentially attack with 4 pieces, Leela had 4 defenders without counting the king. Stockfish's jumped when it opened the h file with its pawns, Leela still thought it was OK.

Leela expected a quick rook exchange on the h file, Stockfish had other ideas and Leela's eval immediately reacted. WIth one black rook in the corner Stockfish saw the opportunity, it exchanged the defending knight and captured the f7 pawn. The black king was caught between the open f and h files and Stockfish saw the mate coming. The game was adjudicated after Stockfish gave its queen for a rook, the PV showed how it could regain the material and win. Two white wins in the opening, Stockfish still leads by +2.

Leela captured a pawn and queens were off early in game 57. Stockfish placed a rook on the 2nd rank and then regained the pawn using a pin on the long diagonal. Stockfish captured another pawn and Leela placed a rook on the 7th file. Evals came down and in a series of exchanges the engines reduced to a RBN vs RR position on move 34. Both kings were exposed to checks by the rooks and the game was adjudicated by the draw rule. In game 58 Leela opened the queen side and after a series of exchanges the game reached a QRB vs QRB position on move 21. After a few pawn moves the engines started to shuffle. Stockfish controlled the open a file but Leela covered the back ranks. Leela's eval kept the game going, Stockfish captured a pawn and avoided the 50-move rule. The engines exchanged more pieces and pawns and the game was adjudicated in a drawn rook ending.

Games 59-60 started with the Alekhine defense modern variation, in a position from a Spassky-Fischer game. After a few early exchanges in game 59 the engines started to play behind their pawn lines. On move 26 Stockfish opened the c file, the engines exchanged all rooks and the game reached a QBB vs QNN position on move 34. Stockfish used its knights to block the open files and the engines started to shuffle. Leela wouldn't lower its eval, near the 50-move rule it reduced to a B vs N ending. Both engines had passers that raced forward, Stockfish was first and Leela lost its bishop for a passer. The black knight was in time to stop the white passers and the game reached a tablebase draw.

In game 60 there was one minor piece exchange after the start, all pawns remained on the board. The engines locked the center and queen side, with a small opening on the king side. Stockfish had more space and its eval was over 1.5, the engines started to shuffle on move 28. On move 73 Stockfish exchanged a pair of pawns on the queen side, its eval came down a llittle and shuffling resumed. On move 101 Stockfish moved a pawn, both engines were playing on increments. Stockfish's eval continued to drift down, it went under 1 for a while and then started to increase after move 140. Leela grabbed a free pawn on the queen side and suddenly Stockfish thought it had something.

The f6 square was vulnerable, Leela had to move its knight to let the king out of the corner. Stockfish exchanged the knight for a bishop and doubled rooks on the g file. Then it forced the g file open with a queen sacrifice and captured h7. The black king had to run away to avoid a back rank mate by the white rooks, and Leela could not stop the white h pawn queening.

Leela captured a knight, but with so much firepower on the back rank Stockfish regained the material quickly. A series of exchanges reduced to a bishop vs pawns ending and a win for white. An unexpected end to a very long game. Stockfish wins the game pair, its lead is +3.

 

Season 19 superfinal games 41-50

After 50 games Stockfish leads 5-4 with 41 draws. Stockfish won a game pair and it leads again, the score was tied since game 24. The match has reached the halfway point, so far there have been only 3 decisive game pairs and 3 double white wins. The engines seem to be of similar strength and the race is very close. 

In both games 41-42 black gave a knight for two pawns after the start, the black king was uncastled in the center and the h file was open for attacking the castled white king. There were many early exchanges in game 41 including the queens, Stockfish did not try to attack the king side. The engines continued to exchange pieces and on move 32 the game reached a N vs pawns position with black 2 pawns up. Evals were close to 0, the advancing black pawns and the white knight canceled out and the game was eventually adjudicated. In game 42 Leela focused on the center, it cleared the white pawns there and created connected passers. Stockfish exchanged pieces and on move 35 the game reached a RNN vs RB position with evals close to 0. Leela lost one central passer and created one on the queen side, the extra white piece was enough for a draw.

Games 43-44 started with a 22-ply book in the Nimzo-Indian Rubinstein variation, a position from games played by Karpov and Tal in 1980. In game 43 Stockfish went a pawn up and Leela castled long. Evals came down, the engines exchanged pieces and Leela regained the pawn. The game reached a double rook ending on move 41, Leela kept postponing the draw rule and the game was finally adjudicated on move 79. In game 44 Stockfish castled short and Leela went a pawn up. Leela gave back the pawn to open the queen side and develop its pieces there. After a few exchanges evals came down, the engines didn't move pawns and the draw rule stopped the game early.

Games 45-46 started with a 2-ply book 1. e4 g6. In game 45 the engines castled in opposite directions. There were many exchanges in a long PV agreement and only RRB vs RRB remained on move 17. The engines locked pawns on both sides and then shuffled for a while. A file opened on the queen side and all rooks were exchanged, leaving a same color bishop ending. Leela wouldn't lower its eval, the game continued until move 129. Game 46 diverged on move 5, the engines again castled in opposite directions. Stockfish pushed pawns on the king side but Leela kept the files closed to protect its king. Leela declined an offer of a rook so that its knight could keep the h file blocked. Stockfish started repeating and its eval came down, then it gave up on the king side and tried to attack the center. It captured a pawn and gave a knight for another pawn, but the attack wasn't strong. Leela traded RR for Q, both evals were close to 0 and the draw rule ended the game.

In game 47 Leela castled long and Stockfish opened a file on the queen side. There were many exchanges after the start and the game reached a QRR vs QRR position on move 29. Stockfish's eval dropped to 0, Leel'a eval also came down and the engines reduced to a rook ending. Leela was a pawn up but Stockfish held the draw.

In game 48 Stockfish castled short and there were no exchanges until move 25. There was a long line of white pawns across the board. Leela pushed pawns on the king side and through a pawn exchange created a pawn majority there, while Stockfish had strong pawns in the center. Stockfish's eval was around 1 from the start, after the queens were exchanged Stockfish's eval jumped over 1.5, it considered Leela's 30th move a blunder. Most of the black pieces were on the king side but the black pawns were between the pieces and the white king. Leela moved its pieces back while Stockfish created a passer in the center.

Leela's eval increased as it realized the danger. Stockfish slowly pushed the central pawns forward, eventually Leela gave a bishop to stop them but it also captured a rook for a knight on the white back rank. The material difference was minimal, both engines had the same number of pawns when the game reached a RBN vs RR position. The evals however showed that Stockfish had a clear advantage.

The white king came forward and captured the h pawn. Leela's last threat was the advanced f pawn, but when it pushed the pawn forward Stockfish was ready with a knight fork and the engines quickly reduced to a RN vs R ending. Stockfish covered the f pawn with its king and the game was over. Stockfish wins a game pair, it leads the match 5-4.

Games 49-50 started with a 2-ply book 1. f4 e5 and continued with white a pawn up. In game 49 the engines developed their pieces without exchanges and evals came down. The exchanges started on move 20, for a while there was a BN vs R imbalance but the engines reduced to a rook ending on move 46. The game continued for 20 more moves until the pawns stopped moving. Game 50 diverged on move 5, though there were few exchanges after the start similar to the reverse game. Stockfish pushed pawns on the queen side, then it offered a knight on the king side but Leela refused to expose its king. After a few exchanges Stockfish gave a rook for a knight and pawn and opened the king side. Leela gave the exchange back and the danger to its king was over. The game reached a same color bishop ending, Stockfish was a pawn up but could only get a draw.