After 10 games Stockfish leads 4-2 with 4 draws. Stockfish won two game pairs, Leela beat Stockfish twice but in both cases Stockfish won in the reverse games.
Openings for the superfinal were prepared by Jeroen Noomen and GM Matthew Sadler, see the details here. The two game pairs that Stockfish won were in Jeroen's list and they were ranked the most drawish. The 3 other game pairs were from Matthew's list and were supposed to be the most biased, yet games 5-6 ended in two draws. Expect the unexpected...
Games 1-2 started with a 20-ply book in the Benoni defense classical variation, played at the highest level of human chess. In game 1 the engines left known theory quickly. Stockfish captured an early pawn but after thinking for 23 minutes its eval jumped. Stockfish gave a rook for a bishop and created connected passers in the center, evals kept increasing. The engines exchanged queens in a long PV agreement, then reduced to a RB vs NN position.
Leela captured the a pawn and created a passer, both engines pushed their passers forward. Stockfish kept its knights behind, it gave its two passers and captured the white a pawn, Leela captured the h pawn.
Leela drove away the black pieces from the king side and captured the last black pawn. Nothing could prevent a queening, game over.
In game 2 the engines took a different path away from theory. For a while Leela's eval was stable, it traded a rook for a knight and pawn, giving Stockfish a central passer. Stockfish surprised Leela and offered a pawn on move 24, after 16 minutes Leela did not take the pawn and its eval jumped. There followed many exchanges, Stockfish captured a pawn and the game reached a RRB vs RNN position.
Leela tried to hold on to its passer while keeping the white rooks back. Eventually the white king came forward and captured the e pawn, allowing Leela to capture a pawn on the king side. Stockfish then slowly pushed the black pieces back, it gave the passer but captured all the remaining black pawns.
Stockfish exchanged minors and offered a rook for a knight, Leela avoided a tablebase win and extended the game to be mated. There were two white wins in this game pair, score is 1-1.
Games 3-4 started with an 18-ply book in the Slav defense, Smyslov variation. In game 3 there were no exchanges after the start, Leela's eval slowly increased. On move 20 Stockfish's eval dropped, it pushed pawns on the queen side and a pawn exchange opened a file. A few moves later Leela's eval dropped as well, the engines exchanged pieces until only QRN vs QRB remained. The game was adjudicated by the draw rule.
In game 4 Stockfish pushed pawns on the king side, where both kings were castled. There were no exchanges and evals were stable until move 24. Stockfish's eval started to jump as it attacked on the king side, Leela thought it was perfectly safe and its eval slowly came down. Stockfish trapped and captured a black knight on the king side, but Leela captured a knight on the queen side. Stockfish's move 32 caught Leela by surprise:
Only now Leela saw the danger to its king and its eval jumped. Leela quickly exchanged pieces and reduced to a RR vs RR position. It went a pawn up and created connected passers on the queen side, but Stockfish had a rook on the 7th rank and two passers, one facing the black king.
Leela exchanged a pair of rooks to prevent two white rooks on the 7th rank. Stockfish stopped the black passers, the white king came forward and the game ended just before mate. Stockfish wins the game pair, it leads 2-1.
In game 5 the engines played a long PV agreement that opened the queen side, Leela was up a pawn with a passer. The game reached a RN vs RN position and evals came down. Leela lost the passer and created another, Stockfish captured the passer on the 6th rank and the draw rule ended the game. Game 6 repeated the same line and diverged on move 19. For a few moves Stockfish's eval jumped, then came back down after the game reached a rook ending. Stockfish was a pawn up but all pawns were on the king side. The evals weren't low enough for the draw rule, the game ended on move 122.
Games 7-8 started with an 18-ply book, a sideline in the Sicilian Scheveningen variation. In game 7 Leela castled long and pushed pawns on the king side, Stockfish still chose to castle short. For a few moves Stockfish's eval increased though the engines followed a PV agreement, then several pieces were exchanged and evals came back down. Leela opened the king side and went a pawn up, the game reached a RN vs RN position and evals dropped. The game was adjudicated when enough pawns have been exchanged.
In game 8 Stockfish again castled long and pushed pawns on the queen side, though the moves were different. Leela castled short and attacked the queen side, evals increased quickly. Leela gave a rook for a bishop in an attempt to keep the king side closed, more exchanges stopped the immediate threat but Stockfish was in control.
Stockfish increased the pressure on the black king, Leela tried to keep its pawns and pieces safe. After a while Stockfish's eval suggested the end was near.
The king side opened and Leela started to lose pieces, mate followed a few moves later. Stockfish wins the game pair, it leads 3-1.
In game 9 evals increased from the start. Queens were off early, Leela castled long and Stockfish kept its king in the center. On move 16 the engines started a long PV agreement that ended on move 29 in a RRB vs RRB position with Leela a pawn up.
The white rooks were more active, Leela managed to get a rook to the 7th rank. Stockfish captured a pawn and created a passer on the king side, while Leela captured 3 pawns on the queen side.
Leela pushed the e pawn forward, Stockfish gave its bishop in an attempt to delay the pawn's advance. This only delayed the inevitable, Stockfish lost a rook for the passer and was later mated.
In game 10 Leela gave a pawn and opened the queen side, as a result Stockfish did not castle its king. Instead Stockfish gave back a pawn and opened a file on the king side, the black king couldn't castle as well and it had no pawn support. Stockfish gave a rook for a knight, it placed two knights on the 5th rank and threatened the black king. Leela gave back a rook for a knight, the game reached a QRN vs QRB position with Stockfish a pawn up.
The white king was also exposed but it managed to find safety using the nearby pawns. Leela had a harder time defending, it exchanged pieces until only the rooks remained and Stockfish captured a second pawn.
Stockfish pushed the b pawn forward, Leela tried to stop it but only delayed the promotion (Stockfish underpromoted to a rook for some reason). Mate followed a few moves later. There were two white wins in this game pair, Stockfish leads 4-2.
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