After 50 games Stockfish leads 5-4 with 41 draws. Stockfish won a game pair and it leads again, the score was tied since game 24. The match has reached the halfway point, so far there have been only 3 decisive game pairs and 3 double white wins. The engines seem to be of similar strength and the race is very close.
In both games 41-42 black gave a knight for two pawns after the start, the black king was uncastled in the center and the h file was open for attacking the castled white king. There were many early exchanges in game 41 including the queens, Stockfish did not try to attack the king side. The engines continued to exchange pieces and on move 32 the game reached a N vs pawns position with black 2 pawns up. Evals were close to 0, the advancing black pawns and the white knight canceled out and the game was eventually adjudicated. In game 42 Leela focused on the center, it cleared the white pawns there and created connected passers. Stockfish exchanged pieces and on move 35 the game reached a RNN vs RB position with evals close to 0. Leela lost one central passer and created one on the queen side, the extra white piece was enough for a draw.
Games 43-44 started with a 22-ply book in the Nimzo-Indian Rubinstein variation, a position from games played by Karpov and Tal in 1980. In game 43 Stockfish went a pawn up and Leela castled long. Evals came down, the engines exchanged pieces and Leela regained the pawn. The game reached a double rook ending on move 41, Leela kept postponing the draw rule and the game was finally adjudicated on move 79. In game 44 Stockfish castled short and Leela went a pawn up. Leela gave back the pawn to open the queen side and develop its pieces there. After a few exchanges evals came down, the engines didn't move pawns and the draw rule stopped the game early.
Games 45-46 started with a 2-ply book 1. e4 g6. In game 45 the engines castled in opposite directions. There were many exchanges in a long PV agreement and only RRB vs RRB remained on move 17. The engines locked pawns on both sides and then shuffled for a while. A file opened on the queen side and all rooks were exchanged, leaving a same color bishop ending. Leela wouldn't lower its eval, the game continued until move 129. Game 46 diverged on move 5, the engines again castled in opposite directions. Stockfish pushed pawns on the king side but Leela kept the files closed to protect its king. Leela declined an offer of a rook so that its knight could keep the h file blocked. Stockfish started repeating and its eval came down, then it gave up on the king side and tried to attack the center. It captured a pawn and gave a knight for another pawn, but the attack wasn't strong. Leela traded RR for Q, both evals were close to 0 and the draw rule ended the game.
In game 47 Leela castled long and Stockfish opened a file on the queen side. There were many exchanges after the start and the game reached a QRR vs QRR position on move 29. Stockfish's eval dropped to 0, Leel'a eval also came down and the engines reduced to a rook ending. Leela was a pawn up but Stockfish held the draw.
In game 48 Stockfish castled short and there were no exchanges until move 25. There was a long line of white pawns across the board. Leela pushed pawns on the king side and through a pawn exchange created a pawn majority there, while Stockfish had strong pawns in the center. Stockfish's eval was around 1 from the start, after the queens were exchanged Stockfish's eval jumped over 1.5, it considered Leela's 30th move a blunder. Most of the black pieces were on the king side but the black pawns were between the pieces and the white king. Leela moved its pieces back while Stockfish created a passer in the center.
Leela's eval increased as it realized the danger. Stockfish slowly pushed the central pawns forward, eventually Leela gave a bishop to stop them but it also captured a rook for a knight on the white back rank. The material difference was minimal, both engines had the same number of pawns when the game reached a RBN vs RR position. The evals however showed that Stockfish had a clear advantage.
The white king came forward and captured the h pawn. Leela's last threat was the advanced f pawn, but when it pushed the pawn forward Stockfish was ready with a knight fork and the engines quickly reduced to a RN vs R ending. Stockfish covered the f pawn with its king and the game was over. Stockfish wins a game pair, it leads the match 5-4.
Games 49-50 started with a 2-ply book 1. f4 e5 and continued with white a pawn up. In game 49 the engines developed their pieces without exchanges and evals came down. The exchanges started on move 20, for a while there was a BN vs R imbalance but the engines reduced to a rook ending on move 46. The game continued for 20 more moves until the pawns stopped moving. Game 50 diverged on move 5, though there were few exchanges after the start similar to the reverse game. Stockfish pushed pawns on the queen side, then it offered a knight on the king side but Leela refused to expose its king. After a few exchanges Stockfish gave a rook for a knight and pawn and opened the king side. Leela gave the exchange back and the danger to its king was over. The game reached a same color bishop ending, Stockfish was a pawn up but could only get a draw.
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