After 70 games Stockfish leads 12-10 with 48 draws. Stockfish extended its lead to 2 wins, this is the biggest lead we've had in this match so far. Stockfish also had a 2 win lead after game 16, before Leela won a game pair of games 19-20. The decisive game pair came after 8 consecutive drawn game pairs, 2 of which were double white wins. This is the first decisive game pair in the second half of the match, there were 9 in the first half.
Games 61-62 started with a 20-ply rare sideline in the KID Orthodox, Korchnoi attack. All pieces and pawns were still on the board with the center blocked. In game 61 there were no exchanges after the start, the engines stabilized the queen side. Starting from move 23 there were a few exchanges, a pair of pawns on the king side, on the queen side a minor piece exchange and another pair of pawns. This opened the a file and the engines exchanged a pair of rooks. Leela created a passer in the center, then the engines mostly shuffled for a while. Evals came down and the engines reduced to a QBB vs QNN position. The engines shuffled until the queens were exchanged and the game was adjudicated. In game 62 again there were no exchanges after the start, after move 20 the engines exchanged minor pieces and opened the b file. Leela was a pawn up with a passer but evals came down. After exchanging a pair of knights Leela gave up its passer and moved its queen and a rook forward on the queen side. Stockfish countered by moving its queen forward too, after exchanging a pair of rooks Stockfish started to give checks. There could have been a quick draw but Stockfish kept delaying with another move. It even gave a rook, but eventually the game ended in a check repetition.
Games 63-64 started in the French Winawer advance variation, played at the highest level of human chess. In game 63 the engines started to play a long PV agreement on move 9, the white king moved without castling and Leela created a pawn majority on the queen side. Leela's eval increased over 1 while Stockfish's eval came down. On move 21 Leela thought for 8 minutes and its eval dropped, despite the fact that Stockfish also moved its king and this trapped a black rook in the corner. There were more minor piece exchanges, Stockfish gave a pawn and created a passer on the queen side. Leela traded a rook for a knight and pawn, also creating a passer on the queen side. In a series of exchanges the engines reduced to a QN vs QR position, Leela was two pawns up but all passers were gone. Leela was not able to find a way to improve, its eval slowly came down and after 45 moves the game was adjudicated.
In game 64 Stockfish pushed pawns on both sides and kept its king uncastled. Leela castled short and Stockfish traded minor pieces and went a pawn up, opening a hole in the black king's pawn support. The engines exchanged a pair of rooks, Stockfish's eval increased slowly while Leela's eval was stable. Leela captured a pawn on the queen side and expected Stockfish to recapture. Stockfish wanted to insert a 2-fold repetition first, Leela decided not to go along and to capture another pawn. This created connected passers for Leela on the queen side, but also allowed Stockfish to capture a pawn and create a passer on the king side, with its queen facing the black king. Stockfish's eval jumped over 2.
Stockfish kept playing 2-fold repetition checks with its queen, slowing the game progress. It gave a knight and captured the black e pawn, creating another passer. Then it captured the black knight, reducing to a QRN vs QRB position. Leela's eval started to increase, its passers looked intimidating but it was unable to push them forward. Stockfish captured one passer, the other reached the 2nd rank. Then Stockfish captured another pawn and the black bishop, while Leela connected a second passer on the queen side again.
Stockfish was a piece up but still had to deal with the black passers. After exchanging queens Stockfish started to see a tablebase win in its PV. Leela captured the white advanced passers, eventually Stockfish gave its knight for the two black passers. The game ended in a winning rook ending with white two pawns up. Stockfish wins the game pair, it leads 12-10.
Games 65-66 started in the Sicilian Kalashnikov variation, played at the highest level of human chess. In game 65 the engines followed theory for a while, they opened the c file and Leela had a pawn majority on the queen side. Leela placed a knight on b6 but Stockfish exchanged it. Stockfish created a passer in the center after exchanging a pair of rooks, evals started to come down. The black queen moved forward, then the engines played out a long PV in which the center pawns were cleared and the game reached a QB vs QB position with white a pawn up. Stockfish gave checks and avoided exchanging queens, it took Leela 60 moves to lower its eval for the draw rule. In game 66 the engines diverged from the reverse game and then transposed back, the real divergence was after 26 plies. Leela was more patient and did not attack the center immediately. After some shuffling Leela opened the e file and Stockfish's eval came down. Stockfish created a passer on the queen side and moved a rook to the 7th rank, Leela avoided exchanges and the engines mainly shuffled with evals close to 0. There was a series of exchanges in a long PV agreement and the engines reduced to a QRB vs QRB position. Stockfish pushed its passer to the 7th rank, Leela threatened mate and Stockfish ended the game in a check repetition.
Games 67-68 started with a 20-ply in a rare line diverging from the Sicilian Velimirovic attack. The engines castled in opposite directions and all pieces were on the board. In game 67 there was a long PV agreement from the start, the engines exchanged minor pieces and pushed pawns across the board without exchanges. Both engines moved rooks to the center, then all rooks were exchanged and Leela went a pawn up. After exchanging queens the game reached a BN vs BB position, the pawns on the king side stabilized and the engines started to shuffle. Leela's eval came down slowly, the game was adjudicated after 45 moves. Game 68 repeated the reverse for 25 plies. Stockfish pushed the h pawn forward and the engines started to shuffle on move 27. The game continued in cycles of shuffles and then a pawn move or a capture that resets the counter. Evals came down very slowly but even when they were low enough there were too many pieces for the draw rule. The game ended in a 50-move draw on move 275.
Games 69-70 started in the Queen's pawn game, Stonewall attack, played in human chess and with a bias for black. In game 69 there were no exchanges after the start, except for a pair of bishops. The first pawn exchange was on move 20, (negative) evals came down. Not a lot happened in the game, in a series of exchanges starting on move 34 the engines reduced to a QN vs QB position. Evals were close to 0 and the game was adjudicated. In game 70 the engines played a different line, again a pair of bishops was exchanged and there were no pawn exchanges after the start. Both queens move forward to the queen side and were exchanged early. Stockfish's (negative) eval came down, the engines opened the g file and Leela kept its king in the center. Leela cleared the white pawns on the queen side, it had two passers there while Stockfish had a passer in the center. The game reached a RRN vs RRN position, Stockfish captured one black passer, then the engines mainly shuffled for a while. Leela's eval came down, after a pair of rooks was exchanged the game was adjudicated.
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