Season 17 superfinal games 91-100

Leela wins the season 17 superfiinal. The final result is 17-12 with 71 draws. There were 7 decisive games in the last 10, Stockfish could still catch up but it lost three game pairs, one of those an unusual double loss. The consolation prize was a game pair win just before the end.

Leela wins for the second time. It missed the superfinal last season, this time it won the premier league and made sure it would qualify. Stockfish had an early lead in the match. Leela equalized and the score was very close in the first 34 games. Leela then won two straight game pairs, took the lead and kept it until the end. The lead extended from +2 to +5 only in the last 10 games.

This season's superfinal was unusual in many ways, (check out my statistics report to see some numbers). The draw rate was 71% which is rather low for a superfinal. This was partly due to the fact that there were many (7) game pairs with two white wins. Perhaps the openings were a bit too biased for this season's finalists? There were 7 games which ended with mate on the board (all Stockfish wins), inconceivable for a superfinal. The games were unusually long even for a superfinal with a NN engine (median of 96 moves per game).

Season 17 started with a change in the CPU hardware. The engines could use 176 threads, and not all engines had this ability. Moreover, the new machine runs on Linux, and Windows based engines had to adapt or run through an emulator. As a result some engines that played in many TCEC seasons dropped out (Fritz, Jonny, Chiron and others). Other engines used less threads and this made them weaker compared to the competition (e.g. Houdini). The GPU hardware was not ready in the first stages of the season and this caused format changes. The qualification league and league 2 were CPU only. League 1 was supposed to be in two parts, one CPU and one GPU, but there were only two GPU contestants and GPU-league 1 was canceled. In the premier league the CPU-only games were played first in order to reduce the time the GPU machine had to be available. All the games were played, but this unusual order lowered the suspense. The GPU engines arrived late and had to catch up the whole division.


Unrelated to chess, the whole season was played with the corona virus in the background. This affected people from all over the world, and was a topic for disscussion in the TCEC chat from time to time. We should be thankful that the TCEC organizers managed to keep the season going under these circumstances.

So, keep up the good work, stay safe, and I hope to be back for season 18.
Go TCEC !!

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Games 91-92 started with the Traxler counter attack in the Italian game, white a pawn up and the black king without the possibility of castling. Evals started over 1 in game 91, Leela's queen came forward and captured the g2 pawn. This opened a file for the white rook, the black king walked to the queen side and Stockfish castled long. Leela pushed a passer to a6 and Stockfish hid its king behind it. Stockfish's eval was over 2 for a while, but nothing seemed to be happening on the board. The engines shuffled and exchanged pieces, and evals came down. On move 53 only QR vs QR remained, Stockfish ended the game in a perpetual check.

In game 92 Stockfish sacrificed a knight and attacked the king side. Leela exchanged queens and gave some material back to get a BN vs R imbalance. The evals increased over 2 as the engines cotinued to exchange pieces, on move 27 only RN vs R remained, Stockfish 2 pawns up.

Stockfish tried to find a defendable pawn formation, its king stayed on the king side to guard the pawns there and Leela focused on the queen side. The black rook couldn't defend all the pawns on its own, eventually Leela managed to capture one.

Leela had only two pawns left, it needed to keep them safe. The next target was the black a pawn, the black rook was outnumbered and the pawn was captured soon enough. Leela was very slow in pushing its passer forward, instead after 40 moves it captured another black pawn. After that Leela's eval went high enough to adjudicate the game on move 130. Leela wins the game pair and extends the lead to +3.

Games 93-94 started with white castling short and black castling long. Stockfish's eval climbed over 2 soon after the start of game 93. It pushed pawns on the queen side and ignored Leela's queen on h3. Leela gave a pawn and opened the center king side. Stockfish exposed the black king and its eval was over 4, Leela was still confident its counter attack was enough to hold.

Leela tried to sacrifice a bishop and expose the white king, Stockfish ignored it and all its pieces chased the black king. Stockfish started to report mate scores as it won material, the game ended on move 43 with the next ply being mate.

In game 94 Stockfish opened a file on the king side, Leela pushed pawns on the queen side facing the black king. Leela targeted the c7 pawn while Stockfish doubled rooks on the h file, nothing happened in both cases. Evals increased and were over 2, Stockfish gave a rook for a bishop (was that necessary?) and the engines exchanged a pair of rooks.

The engines shuffled for a while and then reduced to a R vs N ending on move 48. Stockfish captured a pawn on the queen side and tried to build a fortress. The knight guarded the a7 and c3 pawns, the king was responsible for the f7 pawn. Stockfish's eval was very high, it didn't believe in itself. However, Leela's eval slowly came down as it thought about what to do. The white king had to watch the c3 pawn, the rook kept the black pieces busy. On move 95 Leela gave a pawn on the king side, and then continued shuffling. The real weakness in Stockfish's fortress was the unguarded knight. Leela finally figured this out and brought its rook to drive it away. On move 144 Leela captured the c3 pawn.

Stockfish captured the white a pawn but its fortress crumbled. The engines continued to trade pawns and the game ended in a tablebase win on move 173. Two white wins, very different playing styles. There is no change in the lead.

Evals were below 1 after the start of game 95. There were a few exchanges in the center that weakened the black king side, and Leela castled long. Leela pushed pawns on the queen side, gave a pawn and created a passer there. Evals slowly came down, then turned negative after a pawn trade gave Leela a second connected passer on the queen side.

The black king found safety behind the white a pawn and (negative) evals quicly increased. Stockfish placed its rooks on the queen side to block the passers,  Leela slowly pushed them forward. Stockfish had enough, in a long series of exchanges it gave a bishop to remove the passers. The game reached a R vs RB position on move 59.

Leela kept its single pawn safe, and started to capture white pawns. It captured the a pawn first, then walked with the king to the king side and captured the g pawn. The game was adjudicated when the black passer started to move forward. Leela wins in black against the opening bias.

Leela gave a pawn early in game 96, opening a file on the queen side. Stockfish's king side pieces did not develop and the black king was stuck in the middle. Evals slowly increased, Leela had a space advantage and all pieces were on the board. After several piece exchanges the queen side cleared a little, Stockfish's rook was still stuck on move 34 and the black bishops had almost no moves available.

The black rook got out of its cage on move 44, Stockfish gave the pawn back and tried to open the position. Stockfish gave another pawn, the engines cleared the queen side pawns except for a white passer. After exchanging rooks the game reached a BN vs BN position and Leela captured another pawn to go 2 pawns up.

The material advantage was enough to win. Leela's king walked to the queen side, and the a pawn slowly moved forward. The black pieces had too many targets to defend and they could hardly move. Leela trapped the black bishop and then Stockfish watched as the white king marched back to the king side to capture the bishop. The game was adjudicated a few moves later. Leela wins this game pair from both sides, its lead grows to +5.

Games 97-98 started with a 24-ply book, a popular line in the King's Indian defense, Orthodox variation. In game 97 the engines formed a long diagonal pawn line, then exchanged pawns at both ends of the line and opened the position. Evals came down to 0, starting from move 24 the engines exchanged pieces until only RN vs RB remained on move 35. The game was adjudicated quickly.

In game 98 the engines stayed on popular and drawish lines until move 18. Leela gave a pawn early but other than that there were no exchanges. The center and king side were blocked by a long pawn wall, Leela had more space on the queen side. All the pieces were on the board, Stockfish had a weak backward pawn on c7 and it was hard to move. On move 40 the first minor pieces were exchanged, Leela placed all its major pieces on the b file and evals increased over 1. On move 54 Leela gave a second pawn and opened the b file.

Leela had an entry point, the engines shuffled while Leela considered what to do next. It placed a rook on b7 and arranged its pieces for an attack on the queen side. The exchanges started on move 73, Leela captured the black c and d pawns and the engines reduced to a RB vs RB position.

Stockfish could only block the white passer, its bishop covered the promotion square but it couldn't see the pawn while it was on d7. The engines traded bishops, Leela gave the passer but started to gobble up the king side pawns. The game ended in a winning rook ending with Leela 3 pawns up. Leela wins another game pair, lead extends to +6.

Games 99-100 started with the engines castling in opposite directions. Stockfish pushed pawns on the king side facing the black king in game 99. Leela placed its major pieces on the queen side facing the white king, then opened a file in the center. Evals increased over 1, Stockfish thought its king was safe enough and opened a file on the king side.

Stockfish doubled rooks on the h file and threatened mate. Its eval jumped over 3 when it gave 2 pawns and its queen joined the rooks on the h file. Leela barely held its position and it gave a rook for a bishop and exchanged pieces. On move 42 the game reached a QR vs QB position with Leela a pawn up.

The immediate threat to the black king was over, Leela also had a possible attack on the b2 pawn. Stockfish shifted to the queen side, it captured the black a pawn and pushed its a pawn forward. Leela couldn't stop the passer and Stockfish started to report mate scores. With the black pieces busy looking at the queen side passer, Stockfish returned to chase the black king. It captured the bishop, then was free to promote its passer and finish the game with mate.

In game 100 Leela pushed pawns on the king side, and managed to place a pawn on h6. Stockfish kept the king side files closed and prevented an attack along the long open diagonal, at the price of giving a rook for a bishop. After exchanging queens the game reached a RRB vs RBN position on move 32. Leela created a passer on the queen side, evals went over 1 and the engines shuffled. On move 55 the engines exchanged bishops, Stockfish's eval jumped over 2 for one move and then dropped to 0 when Leela moved. The engines exchanged a pair of rooks and Leela's eval also came down. Stockfish created an advanced passer that was strong enough to compensate for the material. The game ended in a tablebase draw on move 82. Stockfish wins the last game pair, Leela's final lead is +5.

Season 17 superfinal statistics

A summary statistics table of previous stages and seasons. 

Draw rate, wins

 
Final draw rate was 71%.


Game termination

The three most common game termination causes were:

35% - SyzygyTB
35% - TCEC draw rule
12% - TCEC win rule


There were no crashes in the stage. Seven games ended with mate on the board, weird for a superfinal.

Moves per game
 
Median= 96.5
Average= 101.7

Much higher than usual even for a superfinal, the graph is also very unusual. In many games Leela had long shuffle periods, even when it was winning. There were 46 games longer than 100 moves (17 over 150 moves), the longest was 211 moves (Leela - Stockfish, game 58, draw).

Time per game (hours)

 
Median= 3:15
Average= 3:05

The time control was 90 minutes, shorter than usual for a superfinal.

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, 90% of the game pairs repeated the same ECO code, 88% repeated the opening variant. In 94% of the game pairs the ECO first letter was repeated twice. The exceptions were a few very short book sequences of length under 5.

Reverse pairs, wins

 
Reverse pairs, same moves


Pairs of reverse games diverged very quickly, 28% diverged immediately out of book, 66% of the pairs diverged at most after 1 move. The longest repeated sequence of moves was 10 plys (Stockfish - Leela games 79 and 80 that had a 30-ply book opening, Ruy Lopez: closed, Flohr-Zaitsev system, two draws)

Season 17 superfinal games 81-90

After 90 games Leela leads 12-10 with 68 draws. Twice Stockfish won a game and got within one win. Twice Leela immediately won the reverse game. Only 10 games to go, Leela is getting closer to winning the match.

Games 81-82 started with a 24-ply book in the King's Indian defense, Samisch, Bronstein variation, with a Q vs BBPP imbalance. There were many exchanges after the start of game 81, on move 34 the game reached a Q vs RB position. Each engine had 3 pawns, all on the king side. Leela built a fortress and kept the white king away, Stockfish could not make any progress and the game was adjudicated on move 76. More pieces stayed on the board in game 82. Stockfish pushed pawns on the queen side until they met white pawns in a stable formation. After some shuffling Leela traded its queen for a rook and knight and the game reached a R vs B ending with Leela 2 pawns up on move 43. Evals were close to 0 and the engines traded pawns until the game ended in a tablebase draw.

Evals were over 1 at the start of game 83. Stockfish pushed pawns on the king side facing the black king, Leela did the same on the queen side facing the white king. Stockfish gave a pawn and exchanged a pair to open the h file. Its eval jumped to 2.5 when it doubled queen and rook in the open file.

Leela ignored the danger to its king and countered on the queen side. Stockfish traded pawns on the king side to open another file, then it started offering pieces but Leela couldn't afford to capture since any wrong move meant immediate collapse.

In desperation Leela sacrificed a rook to open the queen side and tried to attack the white king. In a spectacular series of exchanges Stockfish gave some material back and then captured the black queen. The game ended with mate on the board on move 46.

In game 84 Leela pushed a pawn to h6 but the king side file stayed closed. The pieces concentrated on the queen side, where Stockfish had two isolated pawns. After some shuffling the engines reduced to a RRN vs RRN position and Leela went a pawn up. Evals were over 1.5 but Stockfish's position looked solid enough.

Leela didn't seem to know what to do next. The engines shuffled for more than 80 moves, with a few pawns moves to reset the draw counter. Both engines were playing on increment and evals slowly came down. On move 133 Leela stopped the shuffle and gave a rook for a knight and pawn. At first evals didn't change too much, then Stockfish grabbed a pawn and evals jumped over 2. The white rook moved to the 7th rank and within a few moves captured two black pawns.

Stockfish tried to counter and threatened the b2 pawn, Leela covered with its knight while its rook captured more black pawns. Leela was 4 pawns up and it started pushing its pawns forward. Eventually Stockfish lost a rook for one of the passers, the game was adjudicated a few moves later. Did Stockfish blunder or was Leela winning the whole time? Two white wins in this game pair, no change in Leela's lead.

In game 85 there were a few exchanges until move 25. Leela pushed pawns on the king side and its king was left without pawn support. Then a series of exchanges opened files on the queen side and cleared the board, Stockfish went a pawn up and Leela placed a rook on the 2nd rank. To avoid back rank threats Stockfish gave a bishop and ended the game in perpetual check. In game 86 all the pawns stayed on the board and the engines played behind the pawn lines. A pair of knights was exchanged on move 21, the queen side stablilized and Leela's eval went over 1. There were a few pawn exchanges after move 39, Leela created a passer on the queen side and a file opened on the king side. Leela couldn't break through the king side, Stockfish's eval dropped to 0. Leela shifted to the queen side and pushed the passer to the 7th rank. Leela shifted back to the king side, Stockfish traded its queen for two rooks and only QB vs RRB remained. Leela's eval also dropped, the engines traded passers and pieces and the game reached a Q vs RB ending and a tablebase draw.

Games 87-88 started with a 4-ply book 1.e4 g6 2.d4 c6. Game 87 transposed into a popular line in the King's Indian defense, Orthodox variation. There were no exchanges after the start, the center was blocked and the engines played behind their pawn lines. Evals came down and it looked like the engines would settle for a draw. After move 33 there were two minor piece exchanges and a file opened in the center. The game was close to adjudication but evals moved away from 0 a little. Stockfish went a pawn up, then a pair of rooks was exchanged, and suddenly Stockfish's eval jumped to 3. Leela saw it was in trouble, in a series of exchanges the engines reduced to a knight ending.

Both engines had connected passers, Stockfish had the advantage since its passers were more advanced, further from the king and and more difficult for a knight to handle. Both kings moved to block the opponent's passers. Stockfish captured one and allowed Leela to capture a pawn on the king side. The two white passers advanced and Stockfish saw it was winning.

Leela stopped one passer but Stockfish sacrificed its knight and promoted the other passer to a queen. The game ended in mate soon after that.

In game 88 the engines played a less popular line in the Modern defense. The engines opened a file on the queen side and later exchanged a pair of rooks, there were a lot of moves behind pawn lines and very few exchanges. Leela's eval was over 1, Stockfish stayed calm until Leela moved a rook and knight forward on the queen side. Stockfish exchanged pieces to get rid of the knight, the game reached a RBN vs RBN position on move 44.

Many black pawns were weak, Stockfish had all its pawns on light squares where the black bishop can't attack them. The white rook on an empty 7th rank was another advantage. Stockfish exchanged rooks, Leela could have taken a pawn on the queen side but decided to switch to the king side. Leela went a pawn up, cleared the king side black pawns and created a passer.

As usual Leela was not in a hurry to push its passer forward. Instead Leela allowed Stockfish to capture one of the h pawns while it captured the queen side pawns. Stockfish gave its knight for a pawn and the game was adjudicated. Another game pair with two white wins, no change in Leela's lead.

Games 89-90 statrted with white down a knight for a rook, with the black king vulnerable on dark squares, and with a white pawn on f6. In game 89 there were many exchanges after the start, Leela gave the material back to stop the attack on its king and only RB vs RN remained on move 26. Evals were close to 0, the engines captured pawns slowly until there was only one black pawn left, and the game was adjudicated. In game 90 Leela castled long and Stockfish weakened the white queen side pawns. Stockfish allowed a white bishop on h6 and captured the f6 pawn. The black queen moved forward on the queen side, when Leela threatened mate on the king side Stockfish ended the game with perpetual check.

Season 17 superfinal games 71-80

After 80 games Leela leads 10-8 with 62 draws. Stockfish won a game pair and reduced Leela's lead to +2, with 20 games remaining. The previous Stockfish win was in game 43 and the previous game pair win was in games 29-30. Can Stockfish make a late comeback?

Games 71-72 started with a 2-ply book 1.e4 Nc6. In game 71 Stockfish forced the black king to move without castling. The king side opened and yet Stockfish castled short. Leela traded its queen for a rook and a knight and on move 28 only QR vs RNN remained, Leela 2 pawns up and with a central passer. Leela pushed the passer to the 2nd rank and Stockfish gave a rook for a knight to remove it. For the rest of the game the engines exchanged a few pawns and shuffled. The game ended in a tablebase draw on move 199. In game 72 the engines castled in oppostie directions, Stockfish pushed pawns on the king side and Leela on the queen side. Both kings lost most of their pawn support and both hid behind an opponent's pawn. Only major pieces remained, the rest of the game was shuffling, trading pawns and pieces. The game ended in a tablebase draw on move 131.

Leela traded both its bishops for knights in game 73 and went a pawn up. Evals came down, Stockfish regained the pawn and the engines exchanged rooks through the open files. The engines continued to exchange all their pieces and the game ended in a tablebase draw on move 49. In game 74 Leela pushed pawns on the king side, it gave a pawn and managed to push one of its pawns to f6. Stockfish's king was in danger and it had a trapped bishop in the corner. It reacted by exchanging pieces, only RRN vs RRB remained on move 26. After the engines exchanged a pair of rooks Stockfish traded its trapped bishop for the two advanced white pawns. In the RN vs R endgame Leela started with 2 pawns to Stockfish's 5. Leela slowly captured black pawns, Stockfish also managed to capture one and each engine had one pawn left on move 58. The engines played the 7-man position until a tablebase draw on move 99.

Queens were off early in game 75, the engines castled late and in opposite directions. The central files were open and the engines exchanged all rooks by move 26. Evals were close to 0 and the game reached a (same color) bishop ending. The game was a draw, it continued until the pawns stopped moving and the evals were low enough. In game 76 both engines castled short quickly. All pieces were on the board until move 26, Leela pushed a pawn to h6 while Stockfish was active on the queen side. Leela's eval jumped over 1 when the queen side became stable, but then the engines started to shuffle. A pawn move reset the 50 move counter, evals slowly came down. Stockfish's queen moved forward, when Leela threatened mate Stockfish ended the game with perpetual check.

Stockfish had an eval over 1 at the start of game 77. It had a bishop pair while Leela had two knights, and it also went a pawn up. The engines exchanged queens and all minor pieces and the game reached a double rook ending on move 23. Both engines had a passer on the queen side, Stockfish pushed its passer forward and its eval jumped over 2 when its passer reached the 7th rank.

Leela remained calm, it blocked the white c pawn with a rook and its passer also moved forward. When the black passer reached the 2nd rank Stockfish's eval started to jump again. The engines traded the passers and a pair of rooks, Stockfish was sure it was winning.

The rook ending with one pawn advantage looked innocent enough, but Stockfish saw far ahead that it had a winning line. The white king came forward, forcing the black rook to move out of the back ranks. Stockfish lost one of the central pawns but managed to take the black e pawn and then the g pawn fell as well. The game ended with mate in Stockfish's PV.

In game 78 Leela had a bishop pair advantage from the start, its eval increasing over 1. Stockfish castled long, the queens were off early and Leela kept its king in the center. Stockfish played defensively, its pieces stayed back and it stabilized the pawn structure. On move 32 the engines started to shuffle, extended to 70 moves by pawns. The engines slowly exchanged pieces and pawns, in a RB vs RN position Leela sacrificed its bishop to create a passer on the 7th rank. Stockfish was prepared to give its rook for the passer, knowing the resulting endgame was a draw. Leela also knew this and kept its passer on the 7th rank, the game continued until Leela gave up the passer, a tablebase draw on move 169. Stockfish wins the game pair and reduces Leela's lead to +2.

Games 79-80 started with a 30-ply book in the Ruy Lopez, Flohr system, played in game 2 of the Kasparov-Karpov match in 1990 and won by Kasparov in white. In game 79 the engines opened files on the queen side, several piece exchanges cleared the board and evals came down to 0. Stockfish went a pawn up and reduced to a QRB vs QRN position on move 43. Leela refused to exchange queens for a while, then the engines reduced to a B vs N ending. Leela lowered its eval close to the 50-move draw and the game was adjudicated. In game 80 all pieces were on the board until move 32. Leela created a central passer on the 6th rank and supported it with its rooks. Not a lot happened until Stockfish blocked the rook support with its bishop. Leela gave a rook for the bishop and Stockfish got rid of the passer, with QB vs QR remaining on move 53 with Leela 2 pawns up. Leela had a queen side passer, but after exchanging queens the endgame was a draw. Leela's eval slowly came down and the game ended in a tablebase draw on move 109.

Season 17 superfinal games 61-70

After 70 games Leela leads 10-7 with 53 draws. The draw streak is over after 21 straight draws. Leela wins a game pair and extends its lead to +3. It has a good chance of winning the match with only 30 games left.

Games 61-62 started with the black queen capturing a (poisoned?) pawn on b2. There were many exchanges after the start of game 61, the game reached a Q vs RB position on move 25. Stockfish was a pawn down, its eval over 1.5 while Leela's eval was low. For a while the engines shuffled and advanced their pawns, on moves 45 and 48 Stockfish's jumped twice and was over 2.5.

Stockfish managed to capture a pawn, other than that it could only give checks. Leela held its position and didn't blunder, Stockfish's eval came down after a long shuffle. The engines exchanged a few pawns and continued to shuffle, Stockfish saw another ghost for a while with evals over 1 and then its eval dropped again. The game was adjudicated on move 190.
In game 62 Stockfish's eval was 0 throughout the game. A few early exchanges opened the position but there were more pieces on the board than in the reverse game. The engines castled in opposite directions, Stockfish attacked on the king side and Leela countered on the queen side. Stockfish exposed the black king and Leela found a perpetual check on the other side, the game ended in a repetition on move 34.

Stockfish's eval was 0 throughout game 63, except for one move. Leela's eval was negative, it pushed pawns on the queen side, then gave a pawn and opened files. The engines exchanged pieces until only QRB vs QRB remained on move 33. Leela had a passer that Stockfish blocked, Stockfish slowly pushed a passer to the 7th rank. The engines traded passers, after some more shuffling Leela captured a pawn and equalized material. The position became stable and Leela's eval came down, the engines exchanged queens and the game was adjudicated. In game 64 Stockfish pushed pawns on the queen side and opened a file. Evals were close to 0, Leela countered on the king side while Stockfish captured two pawns and created passers. Leela gave a knight for pawns, the black king was in danger along the diagonal. When mate was near Stockfish ended the game in perpetual check.

Stockfish placed a knight on c6 early in game 65. Leela managed to get rid of the knight, but it let Stockfish capture a knight for pawns. Both evals were over 1, the white king was exposed and vulnerable. The engines reduced to a RBN vs RB position on move 32, Leela was 3 pawns up and Stockfish only had pawns on the king side. The engines traded the white knight and black bishop, Stockfish needed pawns to win in a RB vs R ending and it had only one left. Stockfish's eval jumped over 2.5 as it captured black pawns, Leela had 2 left that it needed to block the white pawn. The black pawns were accessible to the bishop and Stockfish was optimistic, but Leela kept the white king away and Stockfish couldn't capture a pawn. Stockfish's eval eventually dropped to 0 and the game was adjudicated.

In game 66 Stockfish traded a bishop for a knight early, leaving its king vulnerable on the dark squares. Leela placed its DS bishop on h6 like a thorn bishop, its eval over 1.

Leela gave two pawns and weakened the black pawn structure. Evals increased over 2 and in a series of exchanges the engines reduced to a RB vs R position. Stockfish was 4 pawns up but almost all its pawns were easy targets. Leela had only two pawns left.  

Stockfish captured the white a pawn, but couldn't get the g pawn guarded by the white king. Leela was slow but it managed to capture the black pawns one by one. The game reached a tablebase win on move 94. Leela wins the game pair and its lead increases to +3.

Games 67-68 started with black a knight up for a pawn in the Sicilian Paulsen variation. In game 67 the engines created a Q vs BNN imbalance right from the start. Leela thought it had the advantage, Stockfish's eval was 0. Stockfish avoided exchanging pieces, it pushed pawns across the board to create room for its major pieces. Stockfish had a pawn majority on the queen side, after exchanging a pair of rooks it created an advanced passer. Leela pushed a passer in the center, and in a sequence of moves that involved two white queens for a short while the game reached a Q vs RN position on move 54. Each engine had 3 pawns without passers, after a long shuffle the game ended in a 50 move draw. In game 68 Leela had a different plan, it captured another white pawn and created connected passers on the queen side. The engines reduced to a RR vs RRN position on move 27, Leela pushed its pawns all the way to a6 and b7, where Stockfish blocked them with its pieces. The engines then traded the two white passers and the black knight, exchanging a pair of rooks as well. The result was a rook ending with Stockfish a pawn up, 4 pawns against 3 on the king side. Evals were negative and the game continued on and on, but it was a draw all the way. On move 200 the game was finally adjudicated.

Games 69-70 started with black a pawn up. Leela pushed pawns on the queen side in game 69, Stockfish regained the pawn and Leela controlled an open file. The engines exchanged queens and only rooks and knights remained on move 29. The position became stable, the engines shuffled and pushed a few pawns for 30 moves. The game reached a RN vs RN position on move 66, the engines continued to trade pawns and the game ended in a tablebase draw. In game 70 Leela regained the pawn and the center opened. More pieces stayed on the board, Leela avoided exchanging queens. Evals came down to 0 and the game was adjudicated on move 37 with both engines repeating moves in their PV.
 

Season 17 superfinal games 51-60

After 60 games Leela leads 9-7 with 44 draws. There is no change in the lead Leela has after 10 straight draws. Leela came close to another win but Stockfish held after a long battle.

Stockfish pushed pawns on the king side from the start of game 51, after a few pawn exchanges it had a queen and rook facing the black king. Leela exchanged pieces to stop the attack and evals came down. By move 39 the game reached a QRB vs QRB position. The engines exchanged queens and Stockfish pushed a passer to the 6th rank. Leela exchanged bishops and captured the passer, play continued until reaching a tablebase draw. There were many early exchanges in game 52. Leela gave a rook for a bishop and created an advanced passer on the 6th rank. Only QBB vs QRB remained on move 26, Stockfish blocked the passer and its eval was 0. Leela captured a pawn and created another passer on the queen side, then pushed it to the 6th rank as well. After exchanging queens Leela's eval was over 1, the white king came forward to support the pawns. However, Leela couldn't move its passers forward safely, and it couldn't break the black defense. In the end Leela gave one passer away and the game ended in a perpetual check on move 103.

All pieces were on the board after the start of game 53, only one pair of pawns was exchanged. Leela pushed pawns on the queen side and its eval turned negative. The queen side opened and Stockfish went a pawn up and created a passer. After some shufflng the engines reduced to a RB vs RB position with evals close to 0. The game ended in a tablebase draw. In game 54 the queen side pawn structure was more stable. There were few minor piece exchanges and Stockfish went a pawn up. After the king side pawns stablized the engines shuffled for 40 moves, then exchanges opened the king side and exposed the white king. Stockfish ended the game with perpetual check.

In game 55 a long series of exchanges left only RB vs RB on move 24, and an opposite color bishop ending on move 29. Stockfish was a pawn up, the game continued until move 63 but it was a dead draw. In game 56 the engines castled in opposite directions, a series of exchanges cleared the board by move 25 but there were still enough pieces to play on. However, apart from a few pawn moves the engines shuffled and the game ended in a repetition on move 52.

Game 57 reached a RBN vs Q imbalance after the start. Leela was two pawns up, evals came slowly down. After exchanging a pair of rooks the engines shuffled for a while, Leela gave checks when it could. The engines reduced to a RBN vs Q position on move 49, after exchanging a few pawns Leela created a queen side passer and pushed it to the 2nd rank. Stockfish prevented the pawn promotion and the engines shuffled for 25 moves. The engines started to capture pawns on move 101 until there was only one black pawn left. The game ended in a tablebase draw. Game 58 started similarly, this time reaching a RNN vs Q imbalance. Stockfish was two pawns up, Leela's eval kept increasing. After exchanging rooks Leela's eval was over 2.5, the engines shuffled for a while and then reduced to a RBN vs Q position on move 51. Leela captured a pawn and both evals went over 4.

Stockfish captured a pawn and its eval went down a little. It seemed Leela didn't know how to proceed, there was a long shuffle and Stockfish's eval was around 1. On move 129 the engines exchanged a pair of pawns, Leela had only one pawn left. Stockfish's eval jumped over 2 again, Leela captured a pawn and shuffling started again. After 30 moves Stockfish's eval fell to 0, this time Leela's eval also came down. The engines exchanged another pair of pawns, the game continued for another 35 moves before adjudication. Did Leela miss a win here?

Games 59-60 started with the Fried Liver attack, white sacrificing a knight and the black king on e6. In game 59 Stockfish's eval was over 1 from the start. The black king retreated to the back rank, a few minor pieces were exchanged and Stockfish had a central passer on the 6th rank. Stockfish went 4 pawns up but its eval started to come down. The engines exchanged a pair of rooks, then shuffled for a while. After exchanging the remaining rooks the game reached a QB vs QBN position on move 38, 25 moves later the queens were exchanged. Leela's eval was negative but the position was completely drawn. The game ended in a tablebase position on move 142. Evals were below 1 in game 60, Stockfish's eval dropped to 0 quickly. After a few minor piece exchanges Leela created a central passer on the 6th rank. Leela's eval also dropped, though it had 4 pawns for the knight. The engines continued to exchange pieces and pawns, on move 43 only R vs RB remained. Leela lost its central passer but it pushed 3 connected passers on the king side. Stockfish captured one passer and exchanged rooks, its king and bishop were able to stop the remaining pawns. The game ended in a tablebase draw.

Season 17 superfinal games 41-50

After 50 games Leela leads 9-7 with 34 draws. No change in Leela's lead, the last 10 games
were all draws except one biased opening with two white wins. At the halfway point of the match Leela has a good chance of winning but anything can still happen.

Game 41 started with evals around 1.5. There were no exchanges in the first 30 moves except a pair of bishops, the center was blocked and the engines moved pieces behind their pawns. On move 34 the engines openes a file on the queen side and started to exchange pieces. Then a file opened on the king side and after more exchanges the game reached a rook ending on move 55. Stockfish was a pawn up but the position was drawn, Leela's evals stayed away from 0 and the game ended in a 50-move draw. In game 42 evals were again high at the start, and there were no early exchanges. Leela had a space advantage and it placed a knight on b6, further restricting the black pieces. The engines exchanged minor pieces and evals increased over 2. On move 36 the engines exchanged a pair of pawns, Leela's eval was over 3 and the engines started shuffling. Leela had a few pawn break options but it delayed them for 45 moves. Evals dropped below 2, another pawn pair was exchanged and shuffling resumed for almost 50 moves. After the next pawn move the black queen moved forward and the game ended in a check repetition.

Stockfish's eval was around 2 a few moves after the start of game 43. Stockfish castled long, Leela chose not to castle and it moved all its major pieces to the queen side. Stockfish made sure its king was safe, then it gave a rook for a knight and opened the center.

The black king was in danger and Leela quickly reduced to a BN vs RB position. Stockfish was two pawns up with a strong passer on e6, after exchanging bishops Stockfish gave a pawn and created a second passer on the queen side. It already saw the mate coming.

The white king came forward and Leela couldn't stop both passers. The game ended with mate on the board.

In game 44 Leela castled long and Stockfish castled short, Stockfish traded both its bishops for white knights and evals started to increase. Leela pushed pawns on the king side, one pawn getting to h6. Stockfish had isolated pawns on the queen side, Leela applied more and more pressure until it was able to capture a pawn on move 47.

The a pawn was a dangerous passer, and Leela had a mate threat on the king side. Stockfish got rid of the thorn pawn, at the cost of losing another pawn on the queen side. After exchanging queens only RRB vs RRN were left, Leela two pawns up.

Leela had 3 passes on the queen side but it took its time pushing them forward. It first focused on the king side to avoid any counter from the black pawns. By move 94 All the black pawns were gone as well as a pair of rooks, and Leela had 3 pawns. The game was adjudicated 20 moves later. There were two white wins in this opening, Leela still has a +2 lead.

The center was blocked in game 45, there were no exchanges until move 18. Evals were close to 0 as the engines opened both sides, after exchanging queens Stockfish gave a rook for a bishop and pawn. Leela moved its pieces forward and left its black king exposed, Stockfish ended the game with perpetual check. In game 46 the first exchange was on move 25, the queen side was blocked and the engines opened a file in the center. Leela's eval was over 1 and the engines started to shuffle. The board was crowded with all pieces still playing, nothing happened except two piece exchanges until move 93. Then in a series of exchanges the engines reduced to a queen ending, Leela kept playing until the game was adjudicated on move 184.

Stockfish pushed pawns on the king side in game 47, after a few minor piece exchanges the king side stablized. Leela's eval was over (negative) 1, after the queen side pawns stabilized as well the engines started to shuffle. Close to the 50 move draw Leela gave a rook for a knight and Stockfish's eval jumped close to 2. However, it was a false alarm since the position remained blocked and the shuffle continued all the way to a 50-move draw. In game 48 evals stayed low. The black queen moved forward early, it captured two pawns on the queen side before queens were exchanged. The position opened with more exchanges, Stockfish was a pawn up and had a passer in the center while Leela had a passer on the king side. In a long series of exchanges Leela gave material and captured the black passer, then promoted its passer to a queen. The result was a Q vs RN position on move 52. Leela was able to capture a few black pawns but nothing more. The game continued until a tablebase draw on move 121.

Games 49-50 started with a 20-ply book in the King's Indian defense, where white gave its queen for a bishop and a knight. In game 49 Leela's eval was negative despite white's material advantage. The white pieces stayed back, Leela created a queen side passer and pushed it forward, its eval increasing. Stockfish blocked the passer on the 3rd rank and the engines started to shuffle. Leela's eval went over 2, it captured a pawn and exchanged a pair of rooks. The shuffling continued and Leela's eval came down, on move 123 the engines started to open the position with exchanges. Stockfish captured the black passer and the game reached a Q vs BNN position. The game continued until it was finally adjudicated on move 193. In game 50 Stockfish captured a rook for a bishop early, getting a more equal Q vs RN imbalance. Leela's eval increased over 1 while Stockfish's eval stayed low. The engines cleared the center, Stockfish was 3 pawns up and the engines started to shuffle. After a while Stockfish slowly pushed a passer on the queen side, stopping on the 4th rank. After a few exchanges the game reached a Q vs RB position on move 96. Leela wouldn't lower its eval and the game continued until a tablebase draw on move 172.

Season 17 superfinal games 31-40

After 40 games Leela leads 8-6 with 26 draws. Leela has a lead of 2 wins for the first time in the match. So far it seems that Leela converts advantages more easily than Stockfish, while Stockfish needs a Leela blunder to win.

Games 31-32 started with a 1-ply book 1. e4. In game 31 the engines played a drawish line in the Ruy Lopez Berlin defense. There were very few exchanges, Leela's eval turned negative from move 15,. The engines started to shuffle on move 26, with a pawn move to reset the 50-move counter. Leela's eval went over 1 and started to come back down. On move 86 the exchanges started, Leela gave a rook for a bishop and two pawns. Evals came down as the engines continued to shuffle and exchange pieces, the game was adjudicated on move 139. In game 32 the engines played a drawish line in the Sicilian Najdorf variation. Stockfish gave a rook for a knight and pawn early, the engines started to shuffle on move 21 with a few pawn moves in between. On move 85 a series of exchanges opened the position, on move 102 only RB vs BN remained with Stockfish 2 pawns up. Evals were over 1 for a while, the engines continued to shuffle and the evals stabilized and then came down. The game ended in a tablebase draw on move 187.

Games 33-34 started with a 22-ply book in the King's Indian Defense, Fianchetto variation. In game 33 Stockfish gave a pawn early and pushed pawns on the king side. The engines exchanged minor pieces and evals came down. Stockfish's eval jumped on move 29, it opened the g file facing the black king and then added a rook on the 7th rank. Stockfish's eval suggested the game was over while Leela was competely calm. The white king was exposed and Leela had advancing pawns on the queen side, Leela was sure it could hold off the attack.

Stockfish took the f7 pawn and Leela started to feel pressure. Leela lost its bishop for the white f pawn, the engines exchanged a pair of rooks and the game reached a QRB vs QR position. Leela had a passer on the 2nd rank, but it didn't compensate for the material and the danger to the black king.

The black queen gave checks as much as it could, Stockfish found the opportunity to get rid of the black passer and to release its pinned bishop. Leela captured a few pawns but its king couldn't escape. Stockfish won material and the game ended just before mate.

Leela gave a pawn early as well in game 34. The black queen was ahead of the pawns on the queen side, and Stockfish struggled to develop its queen side pieces. Leela saw that the black queen was far on the queen side, it pushed a pawn to h6 and placed a knight on d6 before the queen could get back.

Stockfish was under pressure. It gave a rook to get rid of the white knight, then exchanged pieces until only RB vs BN remained on move 46. Leela went after the queeh side pawns and cleared them all.

Stockfish saw it was losing but tried to form a fortress. As usual Leela took its time, it captured a pawn on move 73 and exchanged bishops on move 87. The game ended in a tablebase position. There were two white wins in this opening, the score is still tied.

Games 35-36 started with a 20-ply book in the Sicilian Dragon, Yugoslav attack. In game 35 Stockfish gave a pawn to open the h file, then gave a knight and pushed a pawn to h7. The king side attack gave Stockfish the material back and more, on move 26 it was up a rook for 3 pawns. Leela countered with a pair of connected passers on the king side, Stockfish gave some material back to get rid of them .The game reached a B vs N ending on move 39, Stockfish was a pawn up with all pawns on the queen side. Leela held the draw, though Stockfish continued to play until move 101.

Queens were off early in game 36 and the king side stayed closed. Stockfish pushed pawns on the queen side facing the white king, Leela exchanged a pair of rooks and its eval increased over 2, perhaps a better pawn structure? Stockfish's eval also increased, the engines reduced to a RBN vs RBB position on move 35.

Stockfish had 3 weak pawns that had to be defended, its bishop pair was passive. Leela exchanged its knight for a bishop, and then captured the two black pawns on the queen side while losing one pawn on the king side. 

Leela pushed its pawns forward slowly and Stockfish couldn't stop them. Leela won the black rook for one of the passers and the game was adjudicated soon after that. Leela wins the game pair and goes into the lead.

Games 37-38 started with a 2-ply book 1.c4 Nc6, a weak black reply in the English opening. The engines left known theory in a few moves in game 37. Stockfish pushed pawns on the queen side, Leela opened a file and exchanged a pair of rooks. Evals came down as the engines shuffled with their pieces and advanced pawns on the king side. After a few exchanges Stockfish exposed the black king and ended the game in a series of checks.

Game 38 took a different path, but again left theory quickly. There were only a few exchanges in the opening, it seemed that Stockfish was trying to block the center. Evals increased over 2 as Leela exchanged pieces, opened the position and went a pawn up. The engines exchanged queens on move 25 and only RRB vs RRN remained.

Both kings moved to help defend pawns, Leela doubled rooks on the e file and threatened to push its pawns forward. While Stockfish doubled its rooks there as well Leela shifted quickly to the queen side and captured the a pawn.

Unlike in other games Leela played with a purpose. It started to exchange pawns and open the position, then exchanged a pair of rooks and captured another pawn. Stockfish had no defense, the game was adjudicated in a won rook ending three pawns up. Leela wins a second game pair in a row and increases the lead to 2 wins for the first time in the match. .

In game 39 the center was blocked and Leela pushed pawns on the queen side. Leela gave one pawn and managed to push the other to a2. Stockfish managed to get rid of the passer, leaving only one white pawn on the queen side (an no black pawns). Evals were low and the engines started to shuffle, occasionaly exchanging pieces. On move 54 only QRB vs QRB were left, on move 70 the rooks were also gone. The game ended by Leela in a perpetual check on move 136. In game 40 Stockfish opened the queen side and its eval dropped to 0, where it stayed for the whole game. Leela gave a pawn and managed to place a thorn pawn on f6. After a series of exchanges the game reached a N vs B ending on move 34, Leela's eval was around 1.5. Stockfish had two weak pawns and two pieces to defend them, there was nothing Leela could do. After playing all the safe pawn moves it could Leela exchanged a pair of pawns on move 97. The game continued with a lot of shuffling and a few more pawn exchanges, and ended in a repetition on move 158.

Season 17 superfinal games 21-30

After 30 games the score is tied 5-5 with 20 draws. There were 4 decisive games in a row, one biased opening with two white wins and one game pair win for each engine. This superfinal is one of the closest we've seen in TCEC.

There were many exchanges after the opening in game 21 and the position opened up. Stockfish was a pawn up in a QRB vs QRB position on move 31, its king was more exposed than Leela's and evals were close to 0. The engines exchanged queens and Leela captured the bishop for pawns. The game ended in a R vs RB tablebase draw. In game 22 Leela pushed pawns on the king side and kept its king in the center. It gave a pawn and opened the king side with only one black pawn left to protect the black king. Leela also had a protected passer on d6 that Stockfish had to keep an eye on. After some shuffling Stockfish gave a rook for a bishop to remove the passer. The game reached a QRN vs QBN position on move 46, Stockfish's eval was 0. For a long time nothing happened, the engines exchanged knights and a few pawns. On move 127 the queens were exchanged and the game ended in a tablebase draw not long after that.

Many pawns and pieces were exchanged after the start of game 23. Stockfish was two pawns up but its king was in the center without the option of castling. Evals came down slowly, Leela got one pawn back and the game reached a QRB vs QRN position on move 33. The engines started to shuffle and repeat and the game was adjudicated. There was a network crash in the game, which was later resumed. In game 24 both engines did not castle their kings, queens were off early and Leela was two pawns up. Evals came down, Stockfish got a pawn back and reduced to a RN vs RB position. Evals dropped to 0 and the game ended in a tablebase draw.

Stockfish was a pawn up early in game 25, and it had a protected passer on e6. Leela blocked the passer and focused on the queen side where it had a pawn majority. Leela regained the pawn, then engines shuffled for a while and evals came down. Then Leela gave a pawn and created a queen side passer. When the black passer reached the 2nd rank Stockfish sacrificed a bishop to expose the black king and ended the game in a perpetual check draw.

Queens were off early in game 26, both kings moved and remained in the center. Evals were over 1 despite equal material and what appeared to be a dry position, could be because Stockfish had two isolated pawns on the queen side. Evals increased gradually, Stockfish played defensively and guarded its pawns while Leela tried to find a way through. On move 41 Leela captured a pawn on the king side. The game reached a RRN vs RRB position.

There was a long shuffle, Stockfish cracked and started to push pawns forward. most pawns were exchanged, Stockfish was down to its last one and Leela went two pawns up.

Leela's advantage was decisive but it was in no hurry. By move 110 the engines exchanged a pair of rooks and removed the queen side pawns. It took Leela 45 moves before it started to move its pawns forward, the game ended in a tablebase position on move 181. Leela wins a game pair and takes the lead.

The center was blocked in game 27. Leela pushed a pawn to a6 and opened a file on the queen side. Stockfish pushed the h pawn and concentrated on the king side. The engines exchanged a few pieces, then captured their opponents' forward pawns and the position looked stable.

Nothing happened for more than 30 moves. Suddenly Stockfish's eval jumped over 2, it saw an opportunity to attack when all the black pieces were on the queen side. It gave a pawn and opened the king side, Leela's king faced the white queen and rook with only a pinned pawn as a defender.

Leela tried to defend but its king had nowhere to run. Stockfish sacrificed a knight but soon had the black king in a mating net. Leela lost its queen and rook and the game ended in mate.

In game 28 Leela was strong on the king side and Stockfish concentrated on the queen side, similar to the previous game. Only a pair of pawns was exchanged, all the pieces remained on the board for 36 moves. Evals increased all the time, Stockfish's king side pieces were undeveloped and its king remained in the center. Leela gave a pawn and opened the queen side. At first Stockfish had a pair of connected passers but then Leela took one of the passers and exchanged rooks.

The black king was out in the open, it walked to the queen side with pieces surrounding it. On the king side Leela had a constant threat on the black pawns and Stockfish kept its rook and bishop there to defend. Leela had a significant advantage but it took its time. It pushed its king side pawns very slowly with long shuffle periods between pawn moves. On move 121 the queens were exchanged, and on move 138 Leela captured the black passer and went a pawn up.

Finally Leela opened the king side and trapped the black rook in the corner. The white king infiltrated through the king side, Stockfish gave its rook to stop a passer and the game reached a tablebase draw on move 181. There were two white wins in this game pair, though the games were very different. Leela remains in the lead.

Stockfish had an eval of about 1 from the start of game 29. The engines opened a file on the queen side, all pieces were on the board until move 23, then through a series of exchanges the engines reduced to a QRN vs QRB position with Stockfish a pawn up.

For a while evals didn't change a lot, then on move 39 Stockfish's eval jumped over 2.5. Leela remained calm, there did not seem to be a significant change in position but Stockfish was sure it had something. The black queen side pawns were not protected enough and Stockfish managed to capture the a pawn. It was two pawns up with a dangerous passer, Leela still thought it was ok after the rooks were exchanged. 

Leela tried to counter with its queen, but it had to be careful not to allow the white queen attack its king. Stockfish pushed its passer and Leela's eval started to increase. It couldn't handle both the passer and the threat to its king, Leela exchanged the minor pieces. Stockfish saw mate in its PV.

The passer cost Leela its queen, Stockfish even promoted a second pawn before the game was adjudicated.

In game 30 Leela opened a file on the king side, and after exchanging queens it castled long. The game reached a RB vs RB position on move 34. For a few moves Stockfish's eval went over 2, but Leela didn't play according to Stockfish's suggestion. The engines started to shuffle and Stockfish's eval dropped to 0. On move 103 the engines exchanged bishops and reached a drawn rook ending. The game ended in a tablebase draw. Stockfish wins a game pair and the score is tied again.