After 10 games Stockfish leads 3-2 with 5 draws. Leela won the first game pair, then won the next game but Stockfish won the reverse. Stockfish came back with consecutive game pair wins and took the lead. The first 5 game pairs included all the reasonable results, a Leela win, a Stockfish win, a two win draw and two draws. It is unlikely there will be a 2-0 game pair result in the superfinal.
The opening book was created by Jeroen Noomen and GM Matthew Sadler, details can be found here. This season the openings are not ordered by bias, and decisive games should be distributed randomly.
Games 1-2 started with a 12-ply book in the Center game Paulsen attack. In game 1 the engines castled in opposite sides and queens were off early. Leela placed a pawn on f6 through a minor piece exchange, Stockfish felt its king was unsafe and it walked back to the center. Evals were stable, a pawn exchange exposed the white king, for a while the engines shuffled on the queen side. The engines started playing a long PV agreement on move 40, stating with a series of exchanges where Stockfish gave a rook for a knight and attacked the white king. Unexpectedly Stockfish's eval jumped, it felt unsure about the line it thought was safe a few moves before. Leela gave back the material and created a passer on the 7th rank, the game reached a RB vs RB position.
Leela's eval started to increase only after the PV agreement was over on move 56. Stockfish pushed its passer to the 2nd rank but it was blocked there and eventually captured. Leela captured all the remaining black pawns and Stockfish lost its rook for a passer, game over.
In game 2 Leela delayed its castling a little and queens stayed on the board. On move 13 Stockfish thought for 20 minutes and its eval started to drop. Stockfish captured a pawn on the queen side and Leela moved its major pieces there. Stockfish gave back the pawn, Leela had an advanced passer on the a file and the white king hid behind it. The game reached a RB vs RB position with low evals and was adjudicated. Leela wins the game pair, it leads 1-0.
Games 3-4 started with a 20-ply book in the Sicilian Scheveningen, English attack, played at the highest level in human chess. In game 3 the engines followed theory for 17 plys in a PV agreement, Leela captured a pawn and created a pawn majority on the queen side. The engines exchanged queens, Stockfish captured a pawn on the queen side and Leela created an advanced passer in the center. Leela gave a pawn on the queen side, pushed its passer forward and traded it for a bishop.
Stockfish tried to push the h pawn while stopping the white passer, but it couldn't do both effectively. Leela stopped the black pawn on the 7th rank and captured the bishop, the game ended in a tablebase win.
In game 4 Leela left the PV agreement and human theory a little earlier than in the reverse game. Stockfish was a pawn up with a pawn majority on the queen side, this time the queens stayed on the board. Leela regained the pawn on the king side while Stockfish created a passer on b6. Stockfish's eval slowly increased, Leela opened the center and went a pawn up. Stockfish ignored a threat to a rook and connected a passer on the queen side.
Leela delayed as much as it could, Stockfish kept its king safe and slowly pushed the passer forward. After a while Stockfish queened and won. There were two white wins in this game pair, Leela leads 2-1.
Games 5-6 started in the KGA Breyer gambit. The games repeated a 24-ply PV agreement after the start in which all pieces were still on the board, black was a pawn up, the white king moved without castling and the white queen side pieces were not developed. In game 5 the engines mostly shuffled and (negative) evals dropped. Leela developed its queen side and pushed pawns on both sides. After move 36 there were a few exchanges and queens were off. Leela gave a pawn on the king side, Stockfish gave a knight for two pawns and exposed the white king. The game ended in a perpetual check by Leela. In game 6 there were many exchanges after the games diverged, queens were off and Leela had a bishop pair advantage. The black extra pawn was doubled, Stockfish's eval was close to 0. After some shuffling the engines reduced to a drawn rook ending.
Games 7-8 started with a sideline of the KID Averbakh variation. In game 7 there were no exchanges after the start except a pair of bishops, the engines locked the center and castled in opposite directions. Stockfish opened the b file, the white king had no pawn support but Leela kept it safe. The engines shuffled and evals came down, after move 49 the pieces were exchanged gradually and the game was adjudicated.
In game 8 the engines repeated the first 16 plys, there was an additional minor piece exchange but no pawns were exchanged after the start. On move 23 the pawns stopped moving and the engines started to shuffle, Evals remained stable, a pawn move extended the shuffle beyond 50 moves. With both engines low on time, from move 89 Stockfish walked its king across the board to the king side and evals started to increase. On move 107 the white king was in the corner on h1, the 50 move counter was down to 1 and Stockfish was ready to move a pawn to extend it again.
A series of exchanges on the f file reduced to a QN vs RNN position. After a while Stockfish managed to move its pieces forward. Leela tried to attack the white king but was not fast enough. Stockfish captured two pawns, it gave the knight but created two passers on the king side. Leela couldn't prevent a queening and mate. Stockfish wins the game pair, the score is 2-2.
Games 9-10 started in the Pirc, Austrian attack, the book leaving human chess behind. In game 9 the engines opened the d file and queens were exchanged early. Leela moved its king forward without castling, the game reached a RBN vs RBN position on move 23. Evals came down and the exchanges gradually continued, by move 39 only N vs B remained. The engines traded pawns on the king side until they were all gone, the game was adjudicated when evals were low enough.
In game 10 Stockfish kept the d file closed and queens stayed on the board. Evals jumped on move 12, Leela captured a knight on the king side while Stockfish chose to not take a knight. Instead Stockfish pushed a pawn to e6 and added pressure on the black king. Stockfish captured a knight two moves later, Leela managed to capture the e6 pawn to open a way out for its LS bishop. By then Stockfish opened the h file and placed a pawn on g6. Leela traded its LS bishop for a rook yet evals continued to increase, Stockfish was getting ready to attack.
The white knight was hanging but Stockfish threatened mate on h8, Leela's eval jumped. A series of very accurate moves by Stockfish started with a temporary rook sacrifice and resulted in a QN vs Q position. Leela finally captured the g6 pawn, the white knight again was hanging but Leela didn't capture because it led to a faster mate. In the final moves Leela tried to avoid a 7-man tablebase win, it avoided captures. Instead it gave its queen and was mated. Stockfish wins the game pair, it leads 3-2.
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