After 40 games Stockfish leads 11-7 with 22 draws. Leela won a game pair and reduced the gap to 4. In game 31 Leela had a promising position but Stockfish managed to hold the draw. In game 34 Stockfish had a spectacular win with piece sacrifices and a king side attack that Leela didn't see coming, Stockfish had a winning PV on move 27. Game 40 was a slow Stockfish win in an open board, again it took Leela a long time to see it couldn't hold. After 15 game pairs with no double white wins there were 3 in the next 5.
Games 31-32 started with an 18-ply line in the KID Fianchetto, Simagin variation, played in high level human chess. All pieces and pawns were on the board at the start. In game 31 the engines exchanged a pair of pawns on the queen side, a few minor pieces and a pair of rooks. After move 24 evals slowly increased, the engines mostly shuffled and Leela pushed pawns on the king side. Stockfish had less than a minute left on the clock, it used a knight to block the queen side. Leela's eval was over 2 for a few moves and came back down. The engines locked the king side and reduced to a QRN vs QRB position. Stockfish's eval came down as the engines shuffled. On move 95 Leela gave a pawn, its eval also came down. After exchanging rooks the game was adjudicated on move 114. In game 32 Stockfish gave a rook for a bishop but captured a pawn on the queen side and created a passer. Leela's eval slowly came down, Stockfish pushed pawns on the king side and there was one pawn exchange on move 31. There was a long shuffle, on move 78 the engines exchanged minor pieces and then Leela gave back the rook for a bishop. The engines continued to shuffle and Stockfish's eval came down as well. After move 100 evals jumped back a little, the game reached a QRB vs QRN position and the king side opened. Leela went a pawn up but evals came down slowly again, Stockfish regained the pawn but could only shuffle. A series of exchanges reduced to a Q vs R ending, both evals were low and the game was adjudicated on move 167.
Games 33-34 started with a sideline in the Pirc defense, Austrian attack, dragon formation. In game 33 Leela pushed pawns on the king side, after Stockfish castled it moved pieces to the king side to attack the black king. Stockfish captured a pawn in the center, yet evals increased quickly. Stockfish surrounded its king with pieces, with no room to move. The engines exchanged pieces and the game reached a QRB vs QRN position.
The black knight was trapped by its own pawns, while Stockfish tried to get it out safely Leela exchanged queens and regained the pawn. Both engines captured pawns until most of the board was cleared. Leela was up a pawn with connected passers on the king side.
Strockfish couldn't hold on to its pawn, Leela captured it and slowly pushed the passers forward. Stockfish lost the knight for a passer and the game ended in a tablebase win.
In game 34 the engines exchanged a pair of pawns on the queen side, Stockfish moved its queen forward on the king side and Leela captured a pawn, weakening its king safety. Stockfish's eval increased rapidly while Leela thought it was safe. Leela captured two more pawns in the center while the white queen was on h6. On move 21 Stockfish moved its queen side rook to a3, so it could quickly join the attack on the king side. This was not what Leela expected.
Leela's eval started to jump, but too late. Stockfish traded its queen side rook for a knight and moved its two knights forward to join the attack, it already saw a win in its PV. On top of everything Stockfish sacrificed its second rook, temporarily it was down 2 rooks for a knight.
Stockfish chased the black king all the way to the queen side, capturing the black queen for a knight in the process. Leela lost more material and couldn't prevent mate. There were two white wins in this pair, Stockfish leads 9-4.
Games 35-36 started with an 18-ply sideline of the Slav defense, Steiner variation. In game 35 the engines exchanged minor pieces on the queen side. Evals increased a little and then stayed stable for a while, the engines opened the e file with rooks facing each other but did not exchange them. On move 31 Leela captured a pawn.
Leela blocked the e file with a bishop, evals jumped when Leela pushed pawns on the king side. The white king moved forward to support the pawns. Stockfish had to deal with multiple threats to its king and its pieces, on move 47 it gave a rook and countered with an attack on the white king. The king side opened and the white king was exposed, Stockfish also had the white QR in a skewer, but it was down a rook and evals were high in Leela's favor.
Stockfish chose not to take the rook, that would result in a RB vs R ending. Leela gave two pawns on the queen side and the queen moved forward. Stockfish lost more material and was mated.
In game 36 the engines repeated game 35 for 13 plys with a transposition. The engines exchanged a pair of pawns on the queen side, Leela used a bishop to block the files there. Evals were low and mostly stable, the engines mostly shuffled behind their pawns. After move 30 evals started to increase very slowly, on move 54 Stockfish had less than a minute on the clock when it decided it was time to push pawns on the king side.
Stockfish opened the h file and the d file, its queen moved forward to the center of the board and it attacked the black king with a rook through the h file. Leela exchanged queens and captured a pawn, Stockfish created a passer in the center. Stockfish pushed the passer to d6 with bishop support, then doubled rooks on the h file.
Stockfish gave the passer but threatened mate, Leela had to give material to let its king escape to the center. The game reached a RRB vs RB position, the white king moved forward and the game ended in mate. There were two white wins in this pair, Stockfish leads 10-5.
Games 37-38 started with a sideline of the Benoni defense, Hromodka variation. The center was locked and all pieces and pawns were on the board. In game 37 the engines played behind their pawn lines, both engines castled long and seemed to be shuffling with low and stable evals. On move 36 there was a pawn exchange on the king side, then a minor piece exchange on the queen side and evals started to increase. Another pawn exchange on move 46 opened the f file and Leela created a passer in the center. Stockfish pushed the h pawn and created a passer, Leela's eval jumped as all rooks moved to the f file and Leela blocked it with a knight.
There was a long shuffle, the white king moved to the king side. Leela changed its mind on whether to place the king to the right or left of the open f file, in the end the king stayed on g1. Leela moved the knight on f5 and replaced it with a rook. Stockfish captured the rook for a knight, Leela gave another pawn and its second rook moved forward on the f file. The white queen moved to f5, in a series of exchanges Leela traded its rook for two minor pieces.
Stockfish protected its pieces from the white queen, Leela captured two pawns. In desperation Stockfish gave a rook and attacked the white king. When Leela found safety for its king it pushed a passer and queened. Stockfish delayed with checks but was mated.
In game 38 Leela castled short and Stockfish kept its king in the center. Stockfish gave a pawn on the king side, clearing the h file for its king side rook. Evals came down, the white king walked to the king side and Stockfish placed a bishop on h6, then supported it with a pawn on g5. Leela created a passer in the center and pushed it to the 3rd rank. Leela gave a bishop and then captured a rook for a knight. In a series of exchanges Stockfish captured the passer, queens and a pair of rooks were exchanged. Leela reduced to a bishop vs pawns ending, but the white bishop was trapped and the black pawns stopped the white king advance forward. Stockfish could only shuffle and it lowered its eval slowly, the game was adjudicated 20 moves later. Leela wins the game pair, Stockfish leads 10-6.
Games 39-40 started with an 18-ply sideline in the Zukertort, kingside Fianchetto variation. All pieces and pawns were on the board. In game 39 the engines exchanged a pair of pawns on the king side, Stockfish kept its king in the center. Stockfish pushed the e pawn that became a passer, after move 21 evals increased a little. The engines opened the b file and exchanged a few minor pieces, Stockfish's eval came down and then jumped up when it realized that it hadn't planned on Leela's move 28.
Leela captured a pawn on the queen side and created a passer. Stockfish regained the pawn, Leela offered to exchange queens but Stockfish refused to created another advanced passer on the queen side. The black king walked forward to the king side away from the white major pieces. Leela captured a rook and gave a bishop, the game reached a QRR vs QRN position. Leela captured a pawn and created a second passer on the queen side, Stockfish managed to capture both. All pawns were cleared on the queen side.
Leela captured the black passer, its pieces moved forward to attack the black king. The white king was exposed but found safety on the h file. Leela exchanged queens and gained material, the game ended in a tablebase win.
In game 40 the engines repeated game 39 for 13 plys. Leela kept its king in the center but on move 23 it castled short. The engines started to play out a long PV agreement that started with a series of exchanges. Evals came down and the board opened, Leela had a passer in the center while Stockfish had connected passers on the king side. The black king was completely exposed and in danger with so many pieces still on the board.
Leela refused to take the white rook for a bishop, a white bishop pair would be very strong in this position. Leela surrounded its king with pieces, the engines traded pawns until each had two left, white on the king side and black on the queen side. The engines seemed to shuffle but Stockfish's eval slowly increased. The engines exchanged a pair of bishops and Leela pushed its pawns, its eval stayed under 1. Stockfish secured its king, attacked with its queen and rook from one side or the other. On move 84 Leela's eval was still around 1, Stockfish's eval over 3.5.
At this stage Leela's eval jumped, it saw it was unable to hold the position. The white queen and rook continued their attacks until on move 96 Stockfish captured a pawn and the queens were exchanged. Stockfish captured the remaining black pawn, then started to push its pawns forward. The game ended in a tablebase win. There were two white wins in this game pair, Stockfish leads 11-7.
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