After 10 games Stockfish leads 3-1 with 6 draws. Stockfish won the first two game pairs, continuing the trend of the premier division where it won 3/4 game pairs. Then Leela won a game pair, its first win of the season against Stockfish. Stockfish then won a third time and the gap after 10 games is 2 wins. In game 8, the reverse game in the pair Leela won, Stockfish was certain it was winning with eval over 3. Leela's eval stayed low as it steered the game towards a Q vs R ending and built a perfect fortress to hold a draw. It is very unusual to see Stockfish miss this as a draw, its eval remained high for a very long time.
The opening book was created by Jeroen Noomen, details can be found here. Openings were taken from games of chess masters of the past, this season 23 of the openings were from Viktor Korchnoi's games.
Games 1-2 started with a 20-ply line in the Alekhine defense modern variation, played in high level human games. In game 1 the center was locked, there were no exchanges after the start except a pair of minor pieces. On move 24 Leela opened the b file, it captured a pawn and created a passer but evals started to come down slowly. Stockfish blocked the passer with a knight, then placed the other knight on the h file and protected both knights with a bishop on the back rank. The engines exchanged all rooks and started to shuffle, on move 69 the engines exchanged a pair of knights, evals were close to 0. The game was adjudicated 20 moves later.
In game 2 the engines repeated game 1 for 16 plys. The center was locked, Stockfish opened the b file and captured a pawn to create a passer, but in this game evals stayed high though stable. Leela placed its knights on the two board edges like in game 1, but couldn't protect both with a bishop because the c7 pawn blocked the diagonal. The engines shuffled, Stockfish's eval started to increase on move 34, Leela's eval reacted a few moves later.
Leela exchanged pawns on the queen side, the white major pieces moved to the center. The engines started to exchange pieces and pawns on move 44 and the board opened up. After another series of exchanges the game reached a QRB vs QRB position.
Stockfish pushed the passer forward and Leela lost a bishop to stop it. The game ended in a tablebase win. Stockfish wins the game pair, it leads 1-0.
Games 3-4 started with a 22-ply line in the Nimzo-Indian, Rubinstein variation. In game 3 Stockfish opened the e file and gave a rook for a bishop. There were many early exchanges and the game reached a QR vs QB position on move 27. Stockfish blocked the center with a pawn and a bishop and the engines shuffled, Stockfish's eval dropped to 0. On move 46 Stockfish captured a pawn, then Leela gave a pawn and created a passer in the center. Stockfish blocked the passer with a bishop on the back rank, Leela wouldn't lower its eval enough for the draw rule. The engines reduced to a rook vs pawns endgame with black 4 pawns up and the game was adjudicated.
In game 4 the engines repeated game 3 for 21 plys, as in game 3 Stockfish was up a rook for a bishop. Evals jumped when Stockfish pushed pawns on the queen side and moved a rook to the 7th rank. Leela exchanged a pair of rooks and the game reached a QRB vs QBB position.
Stockfish's eval increased slowly while Leela's eval jumped up and down. Stockfish did not take the b7 pawn, probably because it restricted the black LS bishop. Leela controlled the dark squares and had mate threats that Stockfish had to consider, very slowly the white king walked to the center. On move 60 Stockfish pushed the g pawn and opened the g file, then captured the b7 pawn and gave back the rook for a bishop.
The white a pawn became a dangerous passer, Stockfish captured two more pawns and create more passers. Leela captured two pawns and traded bishops, it chased the white king but couldn't avoid a queening. The game ended in a tablebase win. Stockfish wins the game pair, it leads 2-0.
Games 5-6 started with a King's gambit, bishop's gambit variation, with black a pawn up and a bias for black. In game 5 the engines opened the e file, Leela opened the a file and the engines exchanged a pair of rooks. Evals came down as the engines played out a long PV agreement, Leela gave another pawn and created an advanced passer on the queen side. Stockfish captured the passer on the 7th rank, Leela captured a knight for a pawn. The game reached a QBN vs QB position and was adjudicated after queens were exchanged. In game 6 a series of exchanges opened the e file and exchanged most minor pieces. Leela blocked the e file with its bishop, the black pawns stayed back and the engines started to shuffle. Stockfish's eval dropped to 0, Leela's eval came down more slowly. The shuffle was extended with pawn moves, there were too many pieces for the draw rule and the game ended by repetition on move 98.
Games 7-8 started with a 22-ply line in the Torre attack, there was one minor piece exchange and white castled long. in game 7 Stockfish pushed pawns on the queen side and castled long. The engines played out a very long PV agreement, exchanging pawns and knights in the center. Leela had a passer in the center, Stockfish attacked it with many pieces and Leela had enough defenders. After a while the attention shifted to the black pawn on c5.
Stockfish chose to move its bishop to b5 and then protect the c pawn by pushing it to c4. Stockfish gave a pawn on the king side and captured the d passer, Leela shifted focus again and after a pawn trade it created a passer on the e file. Stockfish blocked the passer on the 6th rank, Leela captured the c pawn using a pin and then exchanged queens.
Leela kept its passer protected and exchanged a pair of rooks. Stockfish lost more pawns, the white king moved forward and Leela queened the passer. The game ended in mate.
In game 8 Stockfish thought for 47 minutes on its first move, and chose a different continuation. There were a few pawn exchanges in the center and Leela castled short. Stockfish's eval kept increasing while Leela's eval was low and stable. The black queen moved forward, Stockfish gave two pawns and a knight and opened the g file. Stockfish attacked the black king, Leela exchanged pieces and gave material and the game reached a QR vs RRB position. After exchanging rooks Stockfish pushed a passer and Leela gave the bishop for it.
The resulting position was a black fortress, the black rook could not be moved and it protected the b5 pawn, the white pawns were blocked, the black king was perfectly safe and the white king could not approach the king side. Incredibly Stockfish missed this, its eval was over 3 and wouldn't come down. The engines shuffled until Stockfish's eval was low enough for the draw rule on move 128. Leela wins the game pair, Stockfish leads 2-1.
Games 9-10 started in a Queen's gambit declined sideline, played in human chess. In game 9 Stockfish exchanged minor pieces and queens early. Another minor piece exchange opened the c file and the engines exchanges all rooks through it. The game reached a N vs B ending with almost all pawns on the board, Stockfish's eval was 0 but Leela lowered its eval slowly. The game was adjudicated on move 97.
In game 10 Leela had problems developing its queen side, Stockfish gave a knight and opened the h file. Evals increased quickly as the black king was exposed, Stockfish was a piece down but Leela was playing with two pieces stuck on the queen side and unable to help, so effectively Stockfish had a material advantage attacking the black king.
Leela moved its king to the center and it managed to move its bishop to free its queen side rook. However, the attack wasn't over. Stockfish moved its rook forward, after a few pawn trades the rook gave checks and Stockfish captured the black rook still on a8. The engines then reduced to a queen ending with white a pawn up.
Stockfish used the exposed black king to capture a pawn. Leela did the same with its queen but then Stockfish captured the a pawn and created an advanced passer. Leela lost its queen and the game ended in a tablebase win. Stockfish wins the game pair, it leads 3-1.
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