After 10 games Stockfish leads 4-3 with 3 draws. The match started with 3 game pairs with a win for both engines, an exciting start to the match. The first draw was in game 7, Stockfish won the reverse and the 4th game pair was the first decisive one. The 5th game pair ended in two draws.
The opening book was created by Jeroen Noomen, details can be found here. Most of the openings were taken from games of chess masters of the past.
Games 1-2 started with a 24-ply line in the Queen's Indian defense, Kasparov variation. In game 1 Leela pushed a pawn to h6, Stockfish grabbed a pawn on the queen side, Leela regained the pawn and exchanged queens in the center. The game reached a RRN vs RRB position on move 27, evals started to increase and the engines exchanged all rooks.
The black bishop had only a few pawns it could target and its own pawns restricted its movement. Leela created passers on both sides of the board and blocked a black passer on the 2nd rank. The black king couldn't defend against all the white passers, Leela queened and won.
In game 2 Stockfish also pushed a pawn to h6, there were many early exchanges that opened the board. The game reached a RRB vs RRN position on move 26, the engines exchanged a pair of rooks and traded pawns. The white king moved forward and both engines created a passer on the queen side.
Stockfish blocked the black king away from the queen side. After exchanging rooks the black king moved to help, Stockfish protected its passer and captured the black passer. The white king switched to the queen side and captured pawns there, the game ended in a tablebase win. There were two white wins in this game pair, the score is 1-1.
Games 3-4 started with a sideline of the KID Saemisch variation. In game 3 there were many exchanges after the start with long PV agreements, evals were mostly stable. Leela captured a pawn and created connected passers on the queen side, after queens were exchanged Stockfish moved a pawn to interfere with one of the passers through a capture. On move 33 the game reached a RN vs RB position.
Evals started to increase, Leela pushed the a passer while Stockfish created a doubled passer in the center. Leela gave its a passer but captured more pawns and created passers on both sides of the board.
Leela slowly pushed its passers forward, the connected passers on the king side supported each other and eventually one promoted to a queen. Ten moves later the game ended in a tablebase win.
In game 4 Stockfish kept its king in the center and opened the g file. Most pieces stayed on the board, evals increased steadily. Leela gave a rook for a bishop and tried to protect its exposed king with pieces.
Leela tried to counter with a threat on the f file, Stockfish kept the f3 pawn safe to protect its king. Stockfish offered a rook for a bishop but Leela thought it would weaken its defense. After a few moves Stockfish forced the trade and captured a pawn, the engines reduced to a NN vs BN position on move 45.
Stockfish was a pawn up with a passer, it was confident it was winning but the endgame was long. Leela blocked the passer with its king and protected its isolated pawns. After 15 moves Leela chose to give its bishop for the passer and another pawn. The black king raced to the queen side, there Stockfish trapped it and mated with two knights. There were two white wins in this game pair, the score is 2-2.
Games 5-6 started with a 22-ply line in the Vienna gambit, Fraser-Minckwitz defense, with black a pawn up and white unable to castle, an advantage for black. The black king castled long and there was a white pawn on a6. In game 5 Stockfish gave 3 pawns and opened the king side, with the white king exposed on g3. More pieces joined the attack and (negative) evals increased. The engines exchanged all rooks and Stockfish equalized material, only QNN vs QBN were left on move 33.
Stockfish had a pawn majority on the queen side, it pushed the a and b pawns forward and created a passer. Leela blocked the passer and had to defend against threats to its king and queen. By the time Leela managed to capture the passer Stockfish captured the white g pawn.
Leela was a pawn up and it chose to give a knight for a pawn, Stockfish immediately saw a win. The queens were exchanged, Leela avoided captures but Stockfish reduced to a 7-man win and mated a few moves later.
In game 6 Stockfish blocked the long diagonal with pawns in the center so the black LS bishop would be less effective. Leela placed a pawn on e3 through a minor piece exchange and gave one pawn to open the king side. Stockfish hid its king behind the black pawn.
Leela attacked the long diagonal to open it, Stockfish moved its king back and captured the black d3 pawn. A series of exchanges reduced to a RBN vs RBB position and Leela centralized its bishops, the remaining rooks were exchanged on move 45.
Material was equal but the black bishop pair was very effective and all the white pawns were isolated. Leela captured a pawn and created a pawn majority on the queen side. It took a while before Leela captured another pawn and created a passer. Stockfish lost material trying to block the black pawns, Leela mated with the bishop pair. There were two black wins in this game pair, the score is 3-3.
Games 7-8 started with a 32-ply line in the Ruy Lopez, Chigorin defense, still played in high level human chess. The center and queen side were blocked except the open a file. In game 7 Leela moved a rook forward on the a file, added a second rook and tried to attack. In a long PV agreement the engines exchanges pieces, evals were stable. On move 43 the game reached a QRN vs QRN position, each engine with 7 pawns. The engines shuffled for a while, Stockfish's eval dropped after Leela moved a pawn on the king side. The engines slowly exchanged pieces and pawns, on move 95 the game reached a knight ending. Leela's eval slowly came down, the game was adjudicated on move 116.
In game 8 Stockfish moved a rook forward through the open a file and placed it on c6. Leela moved a knight to attack the rook but Stockfish kept it there, and Leela did not take since the result would be a protected passer on c6. Stockish's eval started to increase and it moved pieces to the king side. On move 32 Stockfish offered a knight on the king side, Leela didn't take but its eval dropped.
For 3 consecutive moves Stockfish's move surprised Leela, Leela spent over 4 minutes per move and still its eval remained low while Stockfish's eval jumped. On move 35 Leela finally understood Stockfish's plan, its eval jumped and the PVs agreed. Both the offered white pieces were taken though material was still equal. The black king was in danger, in another series of exchanges the engines reduced to a RB vs RN position with white 2 pawns up. Leela gave another pawn to create a passer in desperation.
The black passer was quick but Stockfish used a back rank mate threat to capture it. Stockfish gained material, queened a passer and mated. Stockfish wins the game pair, it leads 4-3.
Games 9-10 started with a 20-ply line in the Queen's gambit accepted, Godes variation, where white regained the pawn and both queens moved forward. In game 9 there was a long PV agreement starting from move 16. The engines opened the board, exchanged pawns and a pair of rooks and evals came down slowly. Leela grabbed a pawn, Stockfish countered with a threat on the black king and evals dropped close to 0. In a series of exchanges Stockfish gave a rook and a knight for the white queen, the game was adjudicated a few moves later. In game 10 there were no exchanges after the start, Leela gave a pawn on move 24 and a few moves later the queens were exchanged. The engines slowly exchanged pieces and pawns and evals came down. In a series of exchanges the engines traded R for BB and then reduced to a BNN vs RN position. Then engines shuffled and the game ended in a 50 move draw.
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