Season 18 superfinal games 91-100

Stockfish wins the season 18 superfinal. The final result is 23-16 with 61 draws. This was the expected result and Stockfish increased its lead to +7 despite Leela winning a game pair.

This was the 4th time Stockfish and Leela played in a TCEC superfinal with two wins each. Last season Leela won convincingly, and since that was only 3 months ago I was sure this season would be similar. I was really surprised when the match started with Stockfish winning 3 game pairs in the first 10 games. In the next 40 games the match was more balanced and Leela even reduced the lead to +2. However, Stockfish again won 3 game pairs in 10 games and extended the lead to +5, Leela never recovered from this. Many people had various opinions about why this season Stockfish won / Leela lost the match, fans were either gloating or shouting "scam". In my opinion this was a combination of the hardware, software, opening choices and pure luck. In other words, I have no idea, just enjoying the ride.

Last season I thought a draw rate of 71% was unusually low for a superfinal. This season it was only 61%. This was intentional, Jeroen stated that he preferred more decisive games and his opening choices were more biased than usual. Indeed, there were 11 game pairs with a biased 1-1 result of two white wins.

Looking back at this season, it ran very smoothly compared to last season. The hardware was ready, there were no format changes due to technical limitations. The lower 4 leagues ended very quickly, each was a 1-DRR event with 10 engines and relatively short time controls. The leagues were quite stable in that 7 of the 8 engines that promoted were immediately relegated back in the next league. The premier division started with a possible upset, Stoofvlees led the table after the first DRR one point ahead of Stockfish, Leela and AllieStein. Order was restored when Stockfish beat both AllieStein and Stoofvlees and took the lead. In the end Stoofvlees was only 4th, AllieStein lost a game to Komodo and only managed 3rd place, and we got the classic expected superfinal Stockfish - Leela.

I'm not sure when season 19 will start, there are various bonus events and the TCEC cup that will be played first. I need a break, but with the corona virus in the air no one is going anywhere.

Stay safe, everyone, and Go TCEC !!

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Both engines castled long in game 91, the center was blocked and Leela had more room for its pieces. Leela opened a file on the king side and doubled its rooks there, then the engines shuffled for almost 50 moves before Leela moved a pawn. Most pieces were exchanged and the game reached a RB vs RB position on move 100. Stockfish's eval came down to 0, it reduced to a same color bishop ending. Leela played on, the game was adjudicated only on move 192.

The engines castled short in game 92, then pushed pawns on the queen side. A series of exchanges opened the queen side and left a QRR vs QRR position on move 22. Stockfish's eval was over 2 and increasing, it went a pawn up and it had a central passer.

Stockfish moved a rook to the king side and together with the queen threatened mate in the corner. Evals continued to increase as Leela defended its king and weak pawns. Leela decided to exchange queens and then a pair of rooks. Stocfish was confident the rook ending was a win though material was equal.

Leela couldn't protect both pawns on the 6th rank and Stockfish captured a6 and created a second passer. Leela was able to stop one but Stockfish promoted the other to a queen and won. Stockfish wins the game pair and the lead increases to +7.

All pieces and pawns were on the board until move 20 in game 93. The engines locked the queen side, Stockfish moved its queen forward on the king side. Evals slowly increased while the engines exchanged a few minors, a pair of pawns and the queens. Material was equal but black's pawn structure was worse.

The engines exchanged a pair of rooks, Stockfish tried to hold on to its weak e pawn and Leela exchanged it for its f pawn. Material was still equal but now Leela had a passer, even though it was still on e2. Stockfish's eval was close to 5, reflecting how dangerous it thought the passer was.

Leela exchanged the white knight that blocked the passer. The white king came forward and captured a pawn that the black pieces were too busy to protect. Leela forced the black king out of the way and created a clear path for its passer. The game ended with Leela giving a rook for a bishop to ensure promotion.

Game 94 was more open, there were a few minor piece exchanges after the start and Stockfish kept a bishop pair. The engines opened a file on the queen side, Stockfish let Leela control it while it planted a bishop on d6. Leela went a pawn up and the king side opened, Stockfish's eval increased as it saw a possible attack on the black king. Leela doubled rooks on the queen side, with a pawn on e3 it thought it had a strong enough attack on the white king. Stockfish thought otherwise, its eval jumped over 5.

Leela exchanged a pair of rooks and a pair of bishops, its remaining pieces surrounded the white king. Stockfish went after the black king, every tempo was crucial to the point where Stockfish chose to promote a pawn to a knight with check instead of a queen.

A few moves later the white knight forked the black queen with check, giving Stockfish the win. There were two white wins in this opening, Stockfish's lead is still +7. With 6 games to go Stockfish is officially the winner.

Games 95-96 started in the Russian game, with white sacrificing a knight for two pawns and forcing the black king to move. In game 95 Leela castled long and Stockfish's king completed a short castling by walking to the king side. Stockfish opened the queen side with its pawns, Leela opened a file on the king side. It seemed the black king was more exposed, yet Stockfish's (negative) eval slowly increased. Stockfish gave the piece back and captured a pawn, opening a file and creating a central passer. The engines exchanged a few pieces and Stockfish's eval started to jump. The game reached a QRN vs QRN position on move 47, both engines had advanced passers and material was equal but Stockfish was sure it was much better.

Leela had to protect its pinned knight, as well as move the king safely to remove the pin. Stockfish used the time to capture the white passer, and it covered all squares where Leela could attack the black king. Leela captured the black passer at the cost of losing its knight, Stockfish already saw the win.

The 7-man Q vs QN position was very easy for Stockfish, the game was adjudicated very quickly with the PVs showing how Stockfish can force a queen exchange and win with its knight and last pawn.

Stockfish castled short in game 96 and evals stayed low. Stockfish pushed pawns on the king side and its queen came forward on the queen side. After the king side opened Leela had to protect its king from the white heavy pieces, after exchanging queens Stockfish forced a 3-fold repetition draw. Stockfish wins the game pair and is lead increases to +8.

Games 97-98 started with a 22-ply book, a popular line in the King's Indian Defense, Bayonet attack variation. There were only a few exchanges after the start of game 97, Leela had more space on the queen side and both engines played behind their pawns. After some shuffling evals started to increase, Leela concentrated forces in the center where Stockfish had an isolated pawn. Stockfish decided to give a rook for a bishop and pawn.

Leela attacked the black e pawn and Stockfish defended with all its available pieces. The engines exchanged minor pieces and the game reached a QRR vs QRB on move 55, evals increasing all the time. Leela shuffled for 20 moves before it captured a pawn on the king side and created a passer.

Leela used its pawns to open the king side, Stockfish exchanged queens and Leela captured another pawn. Its two passers on the king side secured the win.

The engines locked the center in game 98, Stockfish pushed pawns on the queen side and opened it with pawn exchanges. Stockfish gave a pawn and tried to attack on the queen side, its eval was over 1 yet not increasing. After exchanging a few minor pieces Stockfish opened another file and regained the pawn, however Leela covered the entry points on the queen side and the engines started to shuffle. After 30 moves the engines exchanged a pair of rooks, then shuffled again. Leela pushed a pawn to the 7th rank, evals came down slowly as the engines exchanged pieces and reduced to an opposite color bishop ending on move 115. The game was adjudicated on move 148. Leela wins the game pair, Stockfish's lead is back to +7.

The engines opened the king side in game 99, Leela castled long and Stockfish did not castle at all. Leela exchanged queens and went up a pawn, then it cleared the black queen side pawns and created 3 queen side passers. Nevertheless Stockfish's eval came down to 0, it regained the pawn and its rooks controlled the back ranks. Leela gave a rook for a knight to keep its bishop pair, the game reached a BB s RB position. Both engines had advanced passers, the game was adjudicated before exchanges led to an opposite color bishop ending. In game 100 the kings' setup was similar, this time the engines opened the king side and most of the queen side pawns remained on the board. After exchanging queens the engines shuffled for a while and evals came down. The game reached a RBN vs RBB position, both engines pushed a passer forward and a series of exchanges led to a rook ending. Stockfish was two pawns up but Leela's single pawn was supported by the king. Leela captured a pawn and the game ended in a tablebase draw.

Season 18 superfinal games 81-90

After 90 games Stockfish leads 20-14 with 56 draws. There was only one decisive game, Stockfish's lead increases to +6. Only 10 games left, Leela is still in the race but with no practical chance of catching up.

In games 81-82 the engines castled in opposite directions. There were many early exchanges in game 81 and the game reached a RRN vs RRB position on move 19. After a few moves the pawns stabilized on the queen side, the engines opened a file on the king side and exchanged a pair of rooks. Stockfish's eval came down to 0 and the engines started to shuffle with a few pawns moves. Leela lowered its eval slowly, the game was adjudicated on move 104. In game 82 Stockfish captured a pawn on the king side and created an advanced passer. Leela exchanged pieces and reduced to a RRN vs RRN position on move 25. Evals were close to 0, both engines had passers that were not strong enough to advance. After exchanging a pair of rooks Stockfish gave the knight for two pawns, the game was adjudicated a few moves later. 

Queens were off early in game 83, the engines exchanged pieces in an open position until only minor pieces were left on move 26. Leela was a pawn up, the engines reduced to a B vs N ending and Stockfish regained the pawn. Evals came down and the game was adjudicated when the pawns stopped moving. The engines exchanged queens early again in game 84, Stockfish forced the black king to move and then the engines reduced to a RRN vs RRN position on move 27. Leela was two pawns up, but its king was exposed and Stockfish chased it all over the board. Evals came down, Stockfish captured pawns and exchanged the rooks. The game reached a drawn knight ending with white a pawn up, and the game was adjudicated quickly.

Stockfish castled long in game 85, Leela moved most of its pieces to the queen side and tried to use a half open file to apply pressure. After some exchanges the game reached a QRB vs QRN position on move 31, Stockfish was a pawn up but Leela had an eval advantage with an advanced passer in the center. However, Leela made no progress and the engines shuffled for a long while. After exchanging queens the shuffling resumed, Leela reset the 50-move counter with a bishop sacrifice. Evals were close to 0 and the game ended in a tablebase draw. Both engines castled long in game 86 and all pieces were on the board until move 25 except a pair of minors. Stockfish created a passer on the king side and pushed it forward. Leela exchanged queens and went a pawn up, then more exchanges led to a RBN vs RBN position on move 33. Leela gave the pawn back and created a passer of its own, Both passers were blocked, Stockfish's eval came down to 0 but Leela captured another pawn and kept trying. The game continued until move 81.

Games 87-88 started in the King's Gambit Accepted, Quade Gambit variant, with black a pawn up. In game 87 Leela pushed a pawn on the queen side and castled short, despite having no pawn cover and a black passer on f3. Leela opened the queen side, took over two files and regained the pawn. Stockfish countered on the king side, it gave a rook for a knight and forced a 3-fold repetition draw.

Stockfish waited for Leela to castle long before it made a move on the queen side in game 88. Leela reacted by trading its queen for 3 minor pieces. Stockfish's eval shot up, after opening a file on the queen side the black king was very close to being mated.

Stockfish captured the knight on g2 and Leela couldn't retake with the bishop since it was a crucial defender. While Leela strengthened its center Stockfish captured a pawn on the king side and pushed its pawns forward. It created a passer which advanced to the 7th rank.

Leela tried to attack the white king, this led to a series of exchanges and the net effect was that Stockfish lost the passer but captured a bishop. The game ended in a Q vs N position. Stockfish wins the game pair and the lead is now +6.

Games 89-90 started with a 20-ply book, a popular line in the Benoni, Czerniak defense variation. In game 89 the engines kept their pawns and the pieces stayed mostly behind the pawn lines. The engines locked the queen side, then opened a file in the center and exchanged a pair of rooks. On move 39 only QNN vs QNN were left and the engines started to shuffle. It took more than 50 moves and a few exchanges for Leela to lower its eval for the draw rule. In game 90 there were only a few exchanges until move 20, then Stockfish pushed a pawn in the center and opened the position. The engines started to exchange pieces and pawns until reaching a rook ending on move 41. Stockfish was a pawn up, but with all pawns on the king side as well as the two kings the ending was a draw. This time Stockfish wouldn't lower its eval and the game continued until move 82.

Season 18 superfinal statistics

A summary statistics table of previous stages and seasons. 

Draw rate, wins

Final draw rate was 61%.

Game termination

The three most common game termination causes were:

51% - TCEC draw rule
37% - TCEC win rule
5% - SyzygyTB, 3-Fold repetition

There were no crashes in the stage.

Moves per game

Median= 64.3
Average= 75.6

There were 16 games longer than 100 moves, the longest was 357 moves (Leela - Stockfish, game 73, draw).

Time per game (hours)

Median= 3:14
Average= 3:08

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, 96% of the game pairs repeated the same ECO code and opening variant. In all the game pairs the ECO first letter was repeated twice. The two exceptions were a few very short book sequences of length under 5.

Reverse pairs, wins

There was an unusual high number of 1-1 results with two white wins, Jeroen's openings were designed to be more biased than usual.

Reverse pairs, same moves

Pairs of reverse games diverged very quickly, 36% diverged immediately out of book, 72% of the pairs diverged at most after 1 move. The longest repeated sequence of moves was 12 plys (Leela - Stockfish games 87 and 88, KGA Quaade gambit, Stockfish wins as white)

Season 18 superfinal games 71-80

After 80 games Stockfish leads 19-14 with 47 draws. Leela won twice, and twice Stockfish won the reverse game. Then Stockfish won a game pair and increased the lead to +5. Only 20 games left, It is very likely that Stockfish will win the match.

Games 71-72 started with the Latvian gambit with a significant advantage for white. In game 71 Leela went a pawn up and queens were off early. Evals increased as the engines developed their pieces, a series of exchanges led to a RRB vs RRB position on move 21.

Leela had a pawn majority on the king side, after exchanging a pair of rooks Leela moved its remaining rook forward to attack the pawns on the queen side. Stockfish tried to defend the pawns and kept the white king away, eventually Leela managed to capture a pawn. 

Once the white pawns started to advance the material advantage was enough for a win. 

In game 72 Leela castled short despite a hole in the pawn protection. On move 12 Stockfish's eval jumped over 3, it sacrificed a bishop and exposed the black king, attacking with its queen and two knights.

The black king was in danger of being mated, Leela had to give a rook for a knight but still the attack wasn't over. Stockfish created a passer and pushed it forward to the 7th rank.

Leela lost a rook to stop the passer, after exchanging queens the game reached a RR vs BN position. Leela's still had an advanced passer, Stockfish lost some material for it but the R vs N ending was a win. There were two white wins in this opening, Stockfish's lead is still +4.

In game 73 there was a few minor piece and one pair of pawns exchanged after the start, the engines played behind long pawn lines. On move 30 the pawns stopped moving and shuffling began. Evals were over 1, Leela's eval peaked at 2, but there was no progress. Leela reset the 50 move counter on moves 77, 125, 171 and 220, then the position opened up and the engines reduced to a RRB vs RRB position. There were a few more exchanges until the end of the game on move 357, close but not a record length for TCEC. In game 74 again there were a few minor piece exchanges after the start, all pawns were on the board until Leela grabbed a pawn on move 19. The engines shuffled for a while and evals came down. The position opened, the white queen moved forward and Stockfish went a pawn up. Leela countered against the white king and captured a rook for a bishop. After exchanging queens Stockfish ended the game in a repetition. 

The engines exchanged most minor pieces early in game 75, evals steadily increased. Leela pushed pawns on the queen side where it had a pawn majority, one pawn made it to the 6th rank. It added a bishop on the 7th rank and Stockfish decided to give a rook and remove both the pawn and the bishop. Only QRR vs QRN were left and evals jumped over 2.5.

Evals continued to increase over 3, but Leela seemed to hesitate and shuffle. The queen side was stable and the focus needed to shift to the king side, however Leela waited for Stockfish to move a pawn and Stockfish wouldn't. The engines entered blitz mode, Leela pushed a pawn to avoid the a 50-move draw. Finally on move 85 Leela threatened mate and forced Stockfish to move the f pawn. After more shuffling Leela's queen moved forward and the white pawns opened the king side. The engines exchanged queens and evals jumped over 6.

The engines traded pawns and Leela created a passer on the queen side. The passer was close to promotion when the game was adjudicated. 

In game 76 the engines cleared the center and Leela went a pawn up. Nevertheless Stockfish's eval was over 1 and slowly increasing, the black king was stuck in the center and Leela decided not to castle and to move it to the king side out of the open center files. On move 24 the game reached a QRR vs QRR position.

Stockfish doubled rooks on the 7th rank, it regained the pawn and after exchanging a pair of rooks it went a pawn up. Stockfish's eval continued to increase while Leela thought it was relatively safe. The engines cleared all the queen side pawns, exchanged rooks and Stockfish captured another pawn to go 2 pawns up in a queen ending.

Stockfish already saw the win, Leela was still hopeful. Leela got one pawn back but the white pawns started to advance and Leela's eval increased as well. Both engines raced with their pawns, both were a square away from promotion. Stockfish's queen kept the black king away from both pawns, so it could stop the black pawn and promote its own. Another opening with two white wins, Stockfish's lead is still +4.

Games 77-78 started with a 20-ply book in the English oening, Symmetrical variation where the black queen moved forward and the white king was forced to move. In both games the immediate continuation involved the white knight forcing the black king to move and capturing a rook with a fork.In game 77 Stockfish's eval jumped on move 17, it drove the white king to the queen side edge and a pair of doubled pawns trapped it there, a kind of vertical "back rank". Stockfish did not take back the knight until move 25, its eval was already over (negative) 3.

Leela captured the pinned black knight but it had to be careful not to get mated. The white bishop was close to being trapped and Leela gave a rook for a bishop to let it out. In a QRB vs QR position Stockfish was 3 pawns up, the black rook joined the attack and again Leela king was in danger. Leela lost material to escape, the game reduced to a rook ending. 

Stockfish was two pawns up, the king side pawns advanced and Leela couldn't stop them. 

Stockfish's eval was 0 from move 15 till the end of game 78. The white king found safety on a2, after Leela took the knight in the corner the engines exchanged most pieces and the game reached a rook ending on move 29. Stockfish pushed a passer to the 7th rank, Leela pushed a passer to the 2nd rank with king support. Both engines could not promote their pawn and they shuffled until Leela lowered its eval for the draw rule on move 78. Stockfish wins the game pair and its lead increases to +5.

There were only a few exchanges after the start of game 79, the center was crowded and Leela tried to push through the queen side. Stockfish placed a knight on e3 that limited the movement of the white pieces. On move 33 a file opened on the queen side and the engines exchanged all rooks throught it, leading to a QB vs QB position. Stockfish's eval came down to 0, Leela had an advanced passer but its exposed king was vulnerable to checks. Leela sacrificed a bishop and went on the attack, after it captured the black bishop Stockfish ended the game in perpetual check. In game 80 Stockfish opened a file on the queen side and moved a rook to the 7th rank .Leela countered on the king side and a series of exchanges reduced to a RB vs RB position on move 29. Stockfish was a pawn up, its eval jumped to 1.5 when it pushed a passer to the 6th rank. It was a false alarm as Leela reduced to an opposite color bishop ending. Stockfish kept the game going until move 121.

Season 18 superfinal games 61-70

After 70 games Stockfish leads 16-12 with 42 draws. Leela fought back and won two game pairs after a long drought (last game pair Leela won was in games 33-34). Stockfish added another game pair to keep the lead at +4. There are only 30 games left, Leela needs wins to stay in the match.

Leela kept its king in the center and pushed pawns on the king side in game 61. Leela had a space advantage, the center was blocked and the black pieces had little room to move. Stockfish moved its queen forward but Leela wouldn't exchange queens. Leela placed a knight on e6 and trapped a black rook, evals were over 2 on move 25.

Stockfish played f6 in an attempt to open some space for its pieces, this opened a path for the white bishop to move behind the pawns via d8 and attack on the queen side. Leela captured a pawn and then found an outpost for the bishop on b6 supported by a pawn. On the king side Leela targeted the g6 pawn.

The engines exchanged queens and Leela went two pawns up, then the game reached a RB vs RB ending. When Leela captured another pawn the game was adjudicated.

There were no castlings in game 62, both kings walked to the king side. All pawns remained on the board until move 23, the engines played behind the pawn lines. Stockfish's eval was over 1 but evals were constant, after locking the king side pawns it seemed the engines shuffled and had no plan. 

Around move 45 evals started to increase, Stockfish saw something but it wasn't clear what that was. Stockfish moved pieces to the queen side and targeted the black b6 pawn.

The white bishop interfered with Leela's heavy pieces that tried to protect the b6 pawn. Stockfish shifted to the king side quickly, opened the block with f4 and attacked with its queen. Leela was caught off guard with its heavy pieces too far to help. Stockfish gave a rook for one of the knights, the black king was in serious danger..

Stockfish captured the weak black passer and blocked Leela's queen route to the king side. Only one black rook came to help the king and that wasn't sufficient, the game was adjudicated as Leela lost material and Stockfish saw the mate coming. There were two white wins in this opening, lead is still +5.

The center was blocked in game 63, all pawns and pieces remained on the board in the first 21 moves. Stockfish castled long and it dominated the queen side, while Leela concentrated forces on the king side. There was one minor piece exchange and the engines started to shuffle, evals were around 1.5 and didn't change for a long time. Only on move 63 Leela moved a pawn to open the king side, Stockfish's eval immediately jumped over 3. 

The effect of the long shuffle was that the rest of the game was played in blitz. Leela captured the h6 pawn and created a 3 to 1 pawn majority on the king side. Stockfish captured a pawn in the center but it gave a rook to stop all the advancing white pawns. After exchanging queens Stockfish tried to build a fortress for its king.

Leela started to shuffle again, evals increased and the game was adjudicated. We didn't get to see how Leela could win but it was a rook up so there probably was a way.

In game 64 Stockfish opened the king side immediately and forced the black king to move. Stockfish castled long and both kings were on the queen side. On move 23 Leela gave a pawn, leading to a series of exchanges including queens that opened the board. Evals came down and the engines continued to exchange pieces, the game reached a drawn rook ending. Leela wins the game pair, Stockfish's lead is reduced to +4.

Stockfish grabbed a pawn early in game 65, allowing Leela to move a bishop to h6 and trap the king. Stockfish then captured a second pawn, evals were positive though as the white pieces were better developed. On move 20 Stockfish attacked the white queen, and Leela surprised with sacrificing the queen for a knight and a bishop. Leela's eval jumped right away, Stockfish's reacted only two moves later. Leela could have gained some of the material back, but with the black king trapped in the corner Leela preferred to keep its attack going.

The black bishop was pinned and was attacked and defended by 3 pieces. Leela moved its free knight forward, and after a few shuffle moves it captured the e6 pawn. Stockfish captured the knight and lost its bishop, the black king used the opportunity to escape from the corner. However, it only managed to move to a new trap on f6, and Leela used a mate threat to capture the white queen for a rook.

The black king was fully boxed in by its own pawns and the white bishop, knight and pawn. The rook on e6 could not move because of immediate mate. Leela waited a few moves without taking it, Stockfish moved its other rook forward to take the f4 pawn but it lost a rook and the game.

In game 66 Stockfish did not castle and its rook protected the h pawn. The engines exchanged pawns and opened the center, another series of exchanges reduced to a double rook ending on move 29. Stockifsh was a pawn up and evals were close to 0. Leela regained the pawn, the engines exchanged a pair of rooks and the game was adjudicated. Leela wins another game pair and Stockfish's lead is now +3.

Both engines castled long in game 67. The black king was a little more exposed, there were many exchanges on the queen side and on move 26 the game reached a QRR vs QRR position. Stckfish's eval came down to 0, the engines shuffled for 20 moves. After trading several pawns and a pair of rooks shuffling resumed and the game was adjudicated.

The engines again castled long in game 68. There were many early exchanges, mostly on the king side, and the game reached a QRN vs QRN position on move 25. The black king was more exposed, Stockfish's eval slowly increased and it was over 2 when the engines exchanged a pair of pawns on the queen side. Stockfish found a safe square for its king, after another pawn trade Stockfish opened a file on the queen side and its eval went over 4.

The white queen and rook could get from one side of the board to the other side very quickly. They chased the black king to the king side and then back to the center. The net result was a very similar position except that the rook and queen switched places. The eval increase showed that this was significant.

Stockfish continued to chase the black king, this time Leela started to lose material. The game was adjudicated with the white rook as the only piece left on the board. Stockfish wins the game pair and its lead increases to +4.

In game 69 Stockfish sacrificed a knight and bishop for 3 pawns, then moved its 3 heavy pieces to the open e file. Stockfish exchanged its rooks for the white queen on the back rank, the game reached a RRB vs Q position on move 31. Stockfish was 4 pawns up and evals were close to 0. Leela captured a few pawns while the black passers advanced, eventually Leela lost the bishop for a passer and the game was adjudicated. In game 70 Stockfish castled early and Leela pushed a pawn to h3. All pieces remained on the board until move 25 and evals were close to 0. Leela opened the queen side and created a passer, then started a series of exchanges with a knight sacrifice. On move 32 only RR vs RB remained, Stockfish had to be careful not to get mated in the corner and Leela used the time to exchange a pair of rooks and protect its passer with the bishop. The black king moved forward, Stockfish ended the game in a repetition draw to prevent a promotion.

Season 18 superfinal games 51-60

After 60 games Stockfish leads 14-9 with 37 draws. Stockfish wons 3 game pairs, increasing its lead significantly. Leela should have won a game pair but it blundered into a very deep winning line that only Stockfish saw.

Stockfish moved its king without castling early in game 51. Leela was a pawn down but had an eval advantage, the black king side rook was trapped in the corner. The engines exchanged minor pieces and Leela regained the pawn. Stockfish released its trapped rook, the game reached a QRB vs QRB position on move 30, Leela had a queen side passer. After exchanging queens Stockfish used its pieces to prevent the passer from advancing After some shuffling the engines exchanged rooks and reached an opposite color bishop ending. Leela was two pawns up but it was still a draw, the game was adjudicated on move 107.

Leela did not castle its king in game 52, the black pieces were mostly on the back rank and the engines played on the queen side. The b file was half open and Stockfish placed a rook there, its eval started to increase when it added a second rook and threatened the black b6 pawn. Leela couldn't defend the pawn, its eval was still relatively low.

After Stockfish captured the b6 pawn the engines exchanged most pieces. Leela soon realized it was in trouble, in a RB vs RB position its rook was still trapped on the king side. By the time the rook broke out it was still on the wrong side of the board. Stockfish gave its bishop and pushed a pawn to the 7th rank, Leela lost its rook to stop it. 

The rook was much stronger in this position, Leela tried to protect its a pawn but Stockfish just traded the rook for the bishop. The white a pawn became a passer and raced forward, promoting first for the win. Stockfish wins a game pair, its lead is now +3.

Games 53-54 started with a 23-ply book, a popular line in the King's Indian, Orthodox variation. Leela pushed a pawn to a6 in game 53, Stockfish pushed pawns on the king side. The engines exchanged all bishops, then Leela's queen moved deep into black territory. Leela captured a pawn but it could not retreat. Stockfish gave a series of queen "checks", Leela's eval came down and the game was adjudicated. In game 54 the setup was similar. Stockfish's eval went over 1 for a while after it opened the queen side and went a pawn up. Leela regained the pawn, evals came down and the engines exchanged bishops and a pair of rooks. The game ended in a 3-fold repetition.

In game 55 the engines castled in opposite directions. Starting from move 10 there was a series of moves following long agreements in the engines' PVs. Most pieces were exchanged and the game reached a RB vs RB position with white a pawn up on move 22. Evals slowly increased, Stockfish moved its king to protect the queen side pawns, its pieces stayed on the king side where Leela had a pawn majority. The engines exchanged rooks, leaving a same color bishop ending. Stockfish's eval was over 4 for a few moves, Leela couldn't find the win and evals came down. The rest of the game was a long shuffle with a few pawns moves and exchanges. The game was adjudicated on move 191.

The engines castled in opposite directions again in game 56. Again there was a series of exchanges with long PV agreements. On move 22 only RRN vs RRB remained, and Stockfish went a pawn up.

Stockfish exchanged a pair of rooks and its eval jumped over 2. The engines traded pawns and Stockfish's eval continued to increase quickly, Leela's eval also started to increase. Stockfish managed to capture all the black pawns and it had two pawns left, one on each side.

The game continued for another 30 moves. Leela delayed the advancing white pawns as much as it could, Stockfish pushed one forward and then the other. Eventually Stockfish found a way to capture the bishop and the game was adjudicated. Stockfish wins the game pair and the lead increases to +4.

Stockfish castled long in game 57, Leela did not castle at all. There were no pawn exchanges after the start, Stockfish's eval came down to 0 and stayed there for the rest of the game. The engines opened a file on the king side and after some shuffling exchanged a pair of rooks. There was a long shuffle starting from move 32, with one pawn move. A few exchanges led to a QRN vs QRB position, then shuffling resumed. Leela lowered its eval for the draw rule on move 126.

The kings' setup was different in game 58, Stockfish as white castled long and Leela castled short. Leela pushed pawns on the queen side while Stockfish gave a pawn and opened a file on the king side, both evals came down. Leela started to plan how to get its king out of the exposed king side, meanwhile it moved its queen to protect a pawn and Stockfish thought that Leela chose the wrong square. It gave a second pawn and opened the center, its eval jumping to around 2.

The black king was out in the open and Stockfish chased it all the way to the b5 square. Leela predicted all these moves in advance yet its eval stayed low. Stockfish had to be careful not to get mated on the back rank, the attack ended with a series of exchanges that left a Q vs RR position.

It took Leela a while to see it was losing. Stockfish pushed the f pawn forward and captured the remaining black pawns. Leela's king was pushed back and Stockfish pushed a second pawn forward before the game was adjudicated. Stockfish wins another game pair, the lead is now +5.

In game 59 Leela appeared to sacrifice its queen for a knight almost immediately at the start. In fact this was the beginning of a combination that included taking the black queen with a pawn. On move 11 Leela was a pawn up with evals over 1.

Leela sent its king to the queen side and developed its queen side pieces. Stockfish gave a pawn to break up the white queen side pawns, its king moved to the king side where there was only one pawn left. The game reached a RRN vs RRN position, Stockfish got one pawn back while evals continued to increase. The engines traded a pair of rooks, all the black pawns were isolated and Stockfish tried to keep them alive.

The white rook moved forward and Stockfish couldn't stop it from taking the queen side pawns. Leela was 3 pawns up with connected passers and the game was adjudicated.

Game 60 started much more quietly. Leela castled its king, Stockfish decided not to since both sides were too exposed. Leela opened a file on the queen side, exchanged a pair of rooks and went a pawn up. Evals remained low, the engines traded R for BN and the black queen moved forward. On move 32 Leela moved its queen, immediately Stockfish's eval jumped to 24 (!!). Leela's eval predicted the next 7 moves correctly, but its eval remained low. Stockfish sacrificed a bishop and exposed the black king.

Stockfish presented 100% tablebase win scores, Leela remained confident it could hold despite the white queen being so close to its king. Stockfish exchanged bishops and moved the passer to e7, Leela had to block with a rook. Stockfish was careful not to allow a perpetual check threat, the knight came forward to protect the passer and threaten mate. Leela soon ran out of checks, its eval was over 2 and it again dropped, really having trouble in understanding the position.

Stockfish captured a pawn and exchanged queens, Leela tried to race to the line but Stockfish threatened mate in the corner, captured the rook and promoted first with check. There were two white wins in this opening, though Leela should have held the reverse. Stockfish's lead remains +5.

Season 18 superfinal games 41-50

After 50 games Stockfish leads 10-8 with 32 draws. Leela got within 1 point twice, and Stockfish won the reverse game in both game pairs. At the halfway point of the match Stockfish keeps a 2 point lead, still quite close and anything can happen. 

Games 41-42 started with a Scotch game modern defense variant, the black queen came forward and the black king moved and could not castle. In game 41 there were many early exchanges and only QRB vs QRB remained on move 18.

Evals slowly increased, Leela was a pawn down but had a better pawn structure, especially on the king side where Stockfish had doubled pawns. The engines exchanged queens and Leela managed to capture all the black pawns on the king side. 

Leela was careful and patient with its king side pawns, after 15 moves Stockfish decided to give its bishop and remove them. Leela had enough pawns left to win a RB vs R ending.

The pieces stayed on the board a bit longer in game 42. After exchanging queens Stockfish had a bishop pair, Leela went a pawn up but Stockfish's eval started to increase. Stockfish traded a bishop for a knight and only RRB vs RRN remained on move 27, Stockfish's eval was over 2.

Stockfish captured a pawn on the king side and created a 3 to 1 pawn majority. The engines exchanged pawns and Leela created 2 passers on the queen side. It pushed a pawn to the 2nd rank and its low eval showed it thought it was relatively safe. Stockfish's eval continued to increase, it controlled the 7th rank with a rook and it was sure it was going to win.

Leela couldn't hold on to the d pawn after the white king moved towards it. The other black passer was too far to be a serious threat, Stockfish doubled rooks on the 7th rank and Leela realized it was going to lose.

Leela avoided an immediate mate but Stockfish captured the knight a few moves later. The game was adjudicated in a RB vs R position with one white pawn to ensure the win. There were two white wins in this opening, lead is still +2.

Game 43 reached a R vs NN imbalance early. Leela was two pawns up, the engines exchanged queens and a pair of rooks and the game reached a RB vs BBN position on move 32. Stockfish's eval came down to 0, the most Leela could do was to give a pawn a get a passer to the 7th rank. Leela continued to play, the game was adjudicated in a R vs BN position on move 78. In game 44 Leela pushed pawns in the center and planted a knight on the 3rd rank. Stockfish exchanged a bishop for the knight and cleared the black central pawns. After a series of exchanges the game reached a RN vs RN position on move 35. Both engines had a pawn near promotion, after a while they traded knights and captured the passers leading to a drawn rook ending. 

In game 45 Leela pushed pawns in the center and Stockfish pushed pawns on the queen side. Evals mostly stayed below 1, Leela waited until move 20 to castle though its king had low pawn cover. Leela surprised Stockfish on move 23 with a pawn move to f5. The white king side completely opened, and then Leela gave a pawn and created an advanced passer in the center. Stockfish's eval jumped over 2, a series of exchanges led to a RBN vs RBN position.

The black knight was almost trapped, Stockfish lost two pawns to save it. While Stockfish concentrated on getting rid of the passer Leela captured another pawn, it was two pawns up in a RN vs RB position on move 49.

Leela drove the black king back and captured another pawn, the game was adjudicated soon after that.

In game 46 Stockfish pushed pawns on the king side and castled short like the previous game. There were several early minor piece exchanges and queens were also off the board. Stockfish's eval started to increase after Leela grabbed a pawn on the queen side and allowed Stockfish to create a pawn majority on the king side. The white king moved forward supporting its pawns and Stockfish placed a bishop and pawn pair deep in black territory. After exchanging a pair of rooks the game reached a RBN vs RBB position and Stockfish went two pawns up.

The black bishop pair was strong, Stockfish's passer could not advance and it was not clear how Stockfish can win, though its eval continued to increase. On move 50 Stockfish traded its knight for a black bishop, then traded rooks and gave its passer to take the black h pawn.

The result was an opposite color bishop ending. Usually a 2 pawn advantage is not sufficient in such an position but this was an exception. The connected pawns needed the attention of both black king and bishop, and by the time Leela captured one pawn Stockfish pushed the c pawn to the 6th rank. Leela could not stop both white passers and Stockfish promoted one to a queen, winning the game. There were two white wins in this opening, lead is still +2.

Leela opened the king side and castled long in game 47. Stockfish exchanged queens and opened the queen side, its eval dropping to 0 though Leela was a pawn up. Only rooks and bishops remained on move 29, both kings were exposed to checks. Leela avoided a repetition draw but the draw rule adjudicated the game. Game 48 started with a similar setup with Stockfish castling long. The white queen came forward and Stockfish tried a king side attack. Leela defended well, it tried to exchange queens but Stockfish refused. After several attempts there was a series of exchanges instead and the game reached a QN vs QB position on move 35. Evals were low, the game continued for 35 moves and was adjudicated when the pawns stopped moving.

Black had an advantage from the opening in games 49-50. In game 49 all the bishops were exchanged by move 16, with all pawns still on the board. Leela didn't castle its king, instead the king walked to the king side. Stockfish's eval came down and it mostly played waiting moves. The engines opened a file on the queen side and exchanged a pair of rooks, after that the game was adjudicated by the draw rule. In game 50 Stockfish castled early and the engines exchanged pawns with all pieces on the board. Leela didn't castle as black, starting from move 21 the engines exchanged pieces and on move 29 only RB vs RB were left with Stockfish a pawn up. The engines mostly shuffled with some pawn moves or captures, Leela slowly lowered its eval. The game was finally adjudicated on move 103, close to a 50 move draw.