After 10 games Stockfish leads 2-1 with 7 draws. Stockfish won two of the first 3 game pairs, then Leela won a game pair and reduced Stockfish's lead to one. Stockfish's first win was a slow eval increase in a position that seemed to be drawn. Its second win was a long Q vs RN ending where Leela (white) thought it was safe for a while. Leela's win was the result of inaccurate moves by Stockfish at the start.
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 18 of the openings were from Mikhail Tal's games.
Games 1-2 started with a variant of the Czech Benoni defense. In game 1 there were many exchanges after the start, the game reached a RN vs RN position on move 23. Stockfish defended a weak backward pawn and didn't allow Leela to invade with its rook. The engines shuffled and evals slowly came down until the game was adjudicated on move 80.
In game 2 there almost no exchanges after the start, the center was blocked and the engines played behind their pawn lines. Stockfish moved its king forward instead of castling, after move 21 there were a few pawn exchanges, then in a series of exchanges the engines opened the queen side and exchanged queens. Evals were low at this stage.
The engines exchanged the remaining pawns on the king side and the white king moved forward. In a series of exchanges the engines reduced to a rook ending and Stockfish saw the win. Using a threat of a back rank mate Stockfish captured a pawn and created a passer. Leela lost the rook and the game ended in a tablebase win. Stockfish wins the game pair, it leads 1-0.
Games 3-4 started with a 24-ply variant of the Sicilian Sozin attack, flank variation. The center white pawns were gone, black was a pawn up but its pieces were mostly on their starting squares. In game 3 Stockfish gave a rook for a bishop and protected its exposed king in the center. Leela thought it had an advantage but its eval dropped when the black king found safety and Stockfish developed its pieces. Leela captured two pawns but after a series of exchanges the game reached an opposite color bishop ending. The engines shuffled and the game was adjudicated on move 105 when Leela lowered its eval. In game 4 Stockfish captured a rook for a bishop though not by the same line as in game 3. Evals came down quickly, the engines exchanged minor pieces and shuffled for a while. The game reached a QRR vs QRB position, Stockfish used check to capture two pawns and created passers on the queen side. Leela countered with an attack on the white king, after sacrificing a rook Leela forced a 3-fold repetition draw.
Games 5-6 started with a 25-ply variant of the King's Indian defense, Saemich variation. There was a Q vs BN imbalance but black had the advantage. In game 5 Stockfish captured two pawns quickly and created a passer in the center. Leela captured the passer and Stockfish exposed the white king with two forward knights. Stockfish also had a strong bishop controlling the dark long diagonal. Leela gave a rook for the black bishop, the game reached a QR vs RRN position with black 3 pawns up.
Leela's (negative) eval drifted down while Stockfish's slowly increased. Leela captured the black d pawn, the engines exchanged a pair of rooks, Stockfish had a pawn majority on both sides of the board. Stockfish slowly pushed pawns on the king side, it created a passer there and another on the queen side after a pawn exchange. Stockfish saw the win but when Leela captured the queen side passer its eval dropped below 1 again.
It took Leela 8 moves to realize it was actually losing. The black king moved forward and Stockfish captured the last white pawn. The white king was trapped and the game ended in mate.
In game 6 Stockfish defended in a different way as white, it exchanged a pair of knights and kept its king safe. Leela gave a rook for a bishop and tried to attack the white king, Stockfish traded a rook for a knight and reduced to a QR vs RBB position. Stockfish placed its pieces on the back rank, the white king moved forward and used black pawns as shields. Stockfish traded its rook for a bishop, the game continued for 30 more moves with Stockfish mostly giving checks until Leela lowered its eval for the draw rule. Stockfish wins the game pair, it leads 2-0.
Games 7-8 started with a 28-ply line in the Ruy Lopez, Chigorin variation. The center was blocked and all pieces and pawns were on the board. In game 7 Stockfish exchanged pawns on the queen side and Leela thought that was a mistake. Stockfish's eval stayed around 1 while Leela's eval increased, by move 27 two files were open on the queen side and the engines exchanged a pair of rooks.
Leela avoided exchanging queens, Stockfish started to see trouble ahead. The engines exchanged the remaining rooks and then Leela captured a pawn and created a passer on the queen side. Leela captured a second pawn, then after a series of exchanges the game reached a BN vs BN position, white two pawns up with connected passers on the queen side.
The engines traded pawns, Stockfish captured one passer and Leela created another on the king side. Stockfish couldn't prevent a queening and the game ended in a tablebase win.
In game 8 the queen side stayed closed, there was only one minor piece exchange after the start and all pawns stayed on the board. Stockfish tried to threaten the king side but nothing came out of it. The first pawn exchange was on move 32, Stockfish created a passer in the center and Leela blocked it. The engines exchanged more minor pieces and evals came down. In a series of exchanges the engines reduced to a rook ending. Stockfish's eval was 0, it took Leela another 20 moves to lower its eval for the draw rule. Leela wins the game pair, Stockfish leads 2-1.
Games 9-10 started with the old Indian defense, Janowski variation. In game 9 there were a few exchanges after the start, the engines opened the e file. The black queen moved forward on the queen side and evals came down. In a series of exchanges Leela captured two pawns and the game reached a QRB vs QRB position. Stockfish captured one pawn back and exchanged queens. The engines traded pawns and Leela regained the pawn, it was two pawns up with two passers but Stockfish managed to capture a pawn and its last pawn was also a passer. Leela pushed one passer to the 7th rank but there it was blocked. The game was adjudicated 20 moves later when Leela lowered its eval. Game 10 repeated 14 plys of game 9, the engines opened the e file. Stockfish grabbed a pawn with its queen, which then became trapped on the queen side. After a while Stockfish freed its queen, the engines exchanged a pair of rooks and then mostly shuffled for a long time. Evals slowly started to increase and were both over 1. On move 98 the game reached a BN vs BN position and then evals dropped. The engines shuffled again and the game was adjudicated. Was this a missed opportunity for Stockfish?
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