After 60 games Stockfish leads 12-3 with 45 draws. Stockfish won two game pairs and increased its lead to 9. It looked like Stockfish would win another game pair, but its eval dropped from 4 to 1 suddenly and the game ended in a draw. Leela hasn't won a game pair, or indeed a game, for a long time. The main question seems to be the lead Stockfish will have at the end of the match.
Games 51-52 started with a 17-ply book sideline of the KID Saemisch variation, with the center pawns locked. In game 51 Leela pushed pawns on the king side and opened the g file, then castled long. Stockfish didn't castle, but walked its king to the king side. The engines exchanged a pair of rooks and a pair of bishops, then started to shuffle with a few pawn moves and exchanges. On move 37 Stockfish went a pawn up, it had a pawn wall across the board except for two files on the king side. Evals came down and the engines reduced to a QN vs QN position. There were too many pawns for adjudication, the game ended in a 50 move draw on move 117. In game 52 Stockfish castled long and Leela castled short, the engines opened the c file. Evals came down as the engines shuffled for a while, including a knight exchange. On move 37 Stockfish captured a pawn, Leela's pieces were active on the queen side facing the white king. Evals dropped to 0, the engines reduced to a double rook ending and Leela regained the pawn. The game was adjudicated when enough pawns were exchanged.
Games 53-54 started in the Caro-Kann, Hillbilly attack variation, with black a pawn up and a black bias. In game 53 Leela chose not to exchange queens, Stockfish's (negative) eval started to increase slowly. In a long PV agreement Leela castled short and Stockfish castled long, Leela pushed a pawn and opened a file on the queen side but its eval started to increase as well. In a series of exchanges the engines reached a material imbalance of QN vs RRB.
Evals were stable for a while and the minor pieces filled the center. Stockfish's eval started to jump, Leela's eval followed 2 moves later. The engines exchanged minors and reduced to a QB vs RRB position, then Stockfish gave two pawns as it formed a winning plan.
The idea was for to use dark squares, the black king moved forward through the center and Stockfish moved a rook to the back ranks. The threat of mate was more dangerous than any white passer that Leela created. After clearing all the queen side pawns both rooks came forward. The white queen tried to help, Stockfish captured it for a rook. The final moves were played only on dark squares, with the white bishop helpless to stop mate.
In game 54 Stockfish chose to exchange queens, forcing the black king to move. The engines played out a PV agreement and evals slowly came down. Stockfish castled long and then evals dropped when in a series of exchanges the engines reduced to a RB vs RB position. Stockfish was a pawn up with a central passer. The engines mostly shuffled for a long time, the game was adjudicated when enough pawns were exchanged. Stockfish wins the game pair, it leads 11-3.
Games 55-56 started with a 16-ply book sideline in the QGA Alekhine system variation. In game 55 the engines exchanged minor pieces and there were no exchanges after that. Stockfish did not castle its king, after move 20 evals came down a little and the black king walked to the king side. There was a period of shuffling and a few pawn moves, on move 48 the engines exchanged minors and resumed shuffling. After move 66 there was a series of exchanges and evals dropped to 0, the game reached a rook ending and was adjudicated. Game 56 started similarly, a minor piece exchange and Leela not castling. On move 17 the engines started a long PV agreement, Stockfish gave a rook for a bishop and two pawns and opened the queen side. Stockfish cleared all the black pawns on the queen side, the game reached a RBN vs RRN position with white two pawns up and two passers, one advanced. Stockfish pushed the passer to the 7th rank, its eval was over 4. Then without warning Stockfish's eval dropped, while playing a move in its PV. In fact Stockfish and Leela predicted the game continuation many plys into the future, but Stockfish suddenly changed its mind about its winning chances. In another PV agreement Leela captured the passer and Stockfish captured a rook for a knight. The engines traded pawns until there were only a few on the king side. It took Stockfish a long time to reduce its eval for the draw rule.
Games 57-58 started with a sideline of the Philidor defence. In game 57 Stockfish pushed pawns on the queen side, Leela pushed pawns on the king side and neither engine castled its king. The engines exchanged minor pieces and evals came down, all pawns were on the board until move 33. The engines shuffled for a while, exchanged a pair of rooks and resumed shuffling. On move 79 Stockfish gave two pawns and moved its queen forward to end the game in check repetition.
In game 58 the engines repeated the reverse game for 21 plys up to transpositions. On move 20 Stockfish went a pawn up and created a passer on the queen side. Leela castled short and Stockfish pushed a pawn and opened the king side. On move 31 all the pieces were still on the board, the engines started to play out a long PV agreement. First queens were off, evals increased as the engines reduced to a RNN vs RBN position.
For a while Leela's eval came down a little, Leela exchanged rooks and regained the pawn. Stockfish's eval jumped higher as it pushed the a pawn forward. Leela was still optimistic after it gave a knight to capture the passer, resulting in a 7-man NN vs B position.
The position was a tablebase win, Leela's eval jumped a few moves later. Stockfish used only 6-man tablebases but it made no mistake and won. Stockfish wins the game pair, it leads 12-3.
Games 59-60 started with a sideline in the Caro-Kann, Bronstein-Larsen variation. In game 59 Stockfish kept its king in the center, there was weak pawn support on both sides. Leela pushed a pawn in the center and it became an advanced passer. The engines opened the queen side and exchanged pieces, evals came down and the game reached a QRR vs QRR position. The game was adjudicated when evals were low enough for the draw rule. In game 60 Leela walked its king to the king side, pieces stayed longer on the board. In a long PV agreement Stockfish gave 3 pawns and opened the center, exposing the black king to attacks. Evals came down, Stockfish got two pawns back and the game reduced to a RB vs RN position. Stockfish had a blocked passer on the 7th rank, the engines traded pawns and Leela captured the passer. The game was adjudicated a few moves later.
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