After 40 games Stockfish leads 5-3 with 32 draws. There were 4 game pairs that ended in double draws, though it is possible Stockfish missed a win in game 34. Then Stockfish won a game pair win, ending a streak of 14 draws.
Games 31-32 started with a 6-ply book in the Scandinavian defense, with the black queen moving forward early. In game 31 Leela pushed the black pieces back. After Stockfish castled Leela gave a pawn on the king side and then castled long. Leela captured a rook for a knight, Stockfish pushed pawns on the queen side and evals came down. The white king hid behind a black pawn, in a series of exchanges the engines reduced to a QR vs QB position. After exchanging queens the pawns raced forward on both sides, but neither engines could force a promotion and the game was adjudicated. In game 32 both engines castled short, there only a few exchanges after the start. Evals came down as the engines played out a long PV agreement, the game reached a queen ending with white a pawn up. Evals were close to 0, Stockfish started to give checks and the game was adjudicated.
In game 33 the engines opened the center, Leela went up a pawn and created a doubled passer on the queen side. Both engines focused on the queen side, evals came down slowly as pieces were exchanged and on move 32 only QRB vs QRB remained. There were a few pawn trades on the king side, then queens were exchanged and the game was adjudicated. In game 34 early exchanges forced the black king to move uncastled. The engines played out a long PV agreement in which Stockfish traded RBN for Q. On move 27 Stockfish's eval jumped over 2.5, the engines reduced to a Q vs RBN position with white 3 pawns up. Leela thought long, about 30 minutes for 4 moves, its eval also increased to around 1. At one point Stockfish's eval was more than 3.5:
However, Stockfish couldn't find a way to break through. Leela blocked the white passers on the queen side with pieces, and built a fortress that the white queen could not penetrate on its own. On move 96 Stockfish traded pawns on the king side, the white king was still blocked and couldn't move forward. Evals slowly came down, pawn moves extended the game until it was finally adjudicated on move 190. Did Stockfish miss an opportunity or was it a mis-evaluation?
In game 35 the center was blocked, Stockfish castled long and Leela kept its king in the center, with evals under 1. Leela gave a pawn on the queen side, opening files for it to threaten the black king. Stockfish kept its king safe and Leela shifted most pieces to the king side. Leela regained the pawn, evals came down enough for the draw rule, despite many pieces on the board. In game 36 the engines opened the center and kept their kings uncastled after the start. In a long PV agreement Stockfish castled long, the engines exchanged pieces until only RRN vs RRB remained on move 25, evals under 0.5. On move 34 Stockfish's eval jumped over 1, but it dropped right back down, not sure what Stockfish saw. The engines continued to exchange pieces until reaching a rook ending, white was a pawn up but it was still a draw.
Games 37-38 started with black a pawn up in the Queen's Gambit Accepted opening. In game 37 Leela regained the pawn and there were no exchanges for a while after the start. The engines opened a file on the queen side and then opened the center, evals came down. All pieces were on the board until move 28, Leela went a pawn up and then the engines reduced to a RB vs RB position. The game was adjudicated when evals were low enough. Game 38 started similarly, this time the center remained closed and the first piece exchange was earlier. The engines exchanged queens and evals came down, the exchanges continued until the game reached a rook ending on move 44. The game ended in a tablebase draw.
Games 39-40 started with a 7-ply book in the Old Indian, Wade variation. In game 39 there were very few exchanges after the start, Stockfish's eval stayed around 1.5. On move 19 the exchanges began, at first opening the center files. Leela's eval increased to around 1, it went a pawn up and then the engines reduced to a RB vs RN position on move 35. Leela didn't seem to have a plan and the engines shuffled for a long while. On move 87 Leela exchanged pawns on the queen side, Stockfish's eval came down quickly to 0. The shuffling continued until Leela lowered its eval, the draw rule stopped the game on move 154.
In game 40 Stockfish pushed pawns on the king side, it gave a pawn and weakened the black pawn structure. Leela castled long while Stockfish kept its king uncastled, the engines played out long PV agreements and Stockfish's eval increased to around 2. A series of exchanges started on move 18, Stockfish regained the pawn and created a passer on the king side. Leela's eval increased over 1 as Stockfish pushed the passer to the 6th rank.
The black bishop was trapped in the corner, it blocked the white passer and was protected by a rook. Stockfish slowly moved its king to the king side to avoid any surprise attack, then it exchanged bishops on move 43.
Leela could not prevent the pawn promotion and it lost its rook. The black queen moved forward to threaten the white king, Leela also created a passer and pushed it forward. This only delayed the inevitable, Stockfish made sure its king was safe, it gained material and finally mated. Stockfish wins the game pair, it leads 5-3.
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