After 30 games Stockfish leads 8-3 with 19 draws. Leela won a game pair and reduced the gap to 2 wins. Then Stockfish won 3 game pairs in a row and extended its lead to 5. It is still early in the match but Leela needs to improve its results to close this gap. It is interesting to note that after 15 game pairs there were 4 double draws and 11 decisive pairs. No pair had two wins, one for each side, which is quite unusual considering that the chosen book openings are biased enough for one of the engines to find a win in 11/15 pairs so far.
Games 21-22 started with a sideline of the Queen's Indian defense, Fianchetto, Nimzowitch attack. In game 21 Leela gave a pawn and opened the center, after a bishop exchange it moved the queen to d6 blocking the black d pawn. The engines agreed on their PV, Stockfish thought long on two moves and its eval started to increase, Leela's eval stayed stable. The black a pawn became a passer, the engines exchanged queens and the remaining bishops and Leela regained the pawn.
The white rooks were more active and the b6 pawn was weak. Leela's eval started to increase, the engines exchanged a pair of knights, then Leela captured the b6 pawn and exchanged a pair of rooks. Stockfish moved a rook forward and managed to capture the white b pawn and equalized material.
Leela attacked the black pawns on the king side with its knight. Stockfish lost only one pawn there but had to abandon its queen side pawn as well. The game ended in a tablebase win.
In game 22 the engines repeated game 21 for 12 plys. The continuation was similar, Stockfish placed the queen on d6 as before, but there were small differences in the location of the other pieces. Stockfish was a pawn down, its queen left d6 and the engines exchanged pieces. Evals came down, Stockfish tried to attack the black king but wasn't strong enough. It managed to regain the pawn, the game reached a double rook ending and was adjudicated. Leela wins the game pair, Stockfish leads 5-3.
Games 23-24 started with an 18-ply line in the Czech Benoni defense. The center was locked and all pieces and pawns were on the board. In game 23 Stockfish thought for 45 minutes on its first move, the engines followed Stockfish's PV and evals drifted down. There was a pawn exchange and a bishop exchange on the king side, for a few moves Leela's eval was close to 1.5 but it came back down after another minor piece exchange. Leela created a passer in the center, Stockfish gave a rook for a knight and captured the passer. The game reached a RR vs RN position and was adjudicated after Leela lowered its eval for the draw rule.
In game 24 Leela thought long on its first move, only 20 minutes this time and it played the same move as Stockfish in game 23. On its next move Leela did not follow game 23, Stockfish's eval started to increase. Stockfish pushed pawns on the king side, trying to open files and attack.
Leela's eval came down for a few moves, there were a few exchanges and Stockfish gave a pawn in the center. Leela's eval jumped back up after 7 moves, Stockfish regained the pawn and opened the f file. Then after a long series of exchanges the game reached a N vs B position.
Leela captured a pawn on the queen side but it took time to create a passer, while Stockfish had a pawn majority on the king side. Stockfish captured the black h pawn with its knight, the engines exchanged minor pieces and both queened a passer. Then Stockfish queened a second passer and mated. Stockfish wins the game pair, it leads 6-3.
Games 25-26 started with a rare sideline in the Queen's Indian accelerated variation. In game 25 the engines followed a long PV agreement, Leela's eval increased to around 1.5 and Stockfish's eval stayed around 1. The engines exchanged minor pieces, Stockfish's eval jumped on move 14 and then came back down immediately, still in PV agreement. After a pawn exchange Stockfish went a pawn up and Leela castled long. In a series of exchanges the engines reduced to a RBN vs RR position with black two pawns up. Only after exchanging a pair of rooks and capturing a pawn Leela's eval started to come down, but it remained too high for the draw rule for a long time. The game was adjudicated on move 100.
In game 26 Leela chose to not exchange its LS bishop, allowing Stockfish to block the long LS diagonal with pawns. There were no exchanges after the start, the engines locked the center, on move 24 there was a first pawn exchange on the queen side. Evals increased as the engines shuffled for a while, on move 33 a pawn exchange opened the h file and the engines exchanged a pair of rooks.
Evals slowly increased as the engines shuffled, Stockfish moved its major pieces to the king side and on move 52 exchanged a pair of pawns there. After another shuffle Stockfish exchanged pawns on the queen side, opened files and moved the rook forward. The engines exchanged rooks and Stockfish captured a pawn, then it captured two more pawns and a series of exchanges reduced to a knight ending.
Stockfish pushed the center pawns forward, queened and mated. Stockfish wins the game pair, it leads 7-3.
Games 27-28 started with a rare sideline of the Scandinavian defense, modern variation, with white a pawn up. In game 27 Leela captured a second pawn, opened the e file and moved the queen forward. Stockfish forced the white king to move without castling and castled its own king. Leela captured a bishop, Stockfish used the exposed white king to capture the white queen for a rook. The game reached a RNN vs Q position with black a pawn up. Stockfish's eval came down, Leela took a long time to lower its eval. The game was adjudicated on move 130.
In game 28 Leela pushed e5 and expected Stockfish to take en passant and move the white queen forward as in game 27. However Stockfish waited, pushed pawns on the king side and exchanged the pawn on e5. The e file opened but the white queen stayed behind, both engines castled. Stockfish's eval slowly increased, Leela's eval stayed around and under 1. The engines exchanged queens and Stockfish created a passer in the center.
Leela's eval started to increase as well, the engines exchanged minor pieces and Stockfish pushed the passer to d6. Stockfish gave a pawn and offered a rook exchange which Leela avoided. The passer arrived to d7 safely and Leela blocked with a rook. Stockfish moved a rook to the 7th rank, Leela captured a pawn and the game reached a RRN vs RRN position, Stockfish saw the win in its PV.
Stockfish captured the black a pawn and captured a rook for a knight. Leela lost the second rook for the passer and the game ended in a tablebase win. Stockfish wins the game pair, it leads 8-3.
Games 29-30 started with a sideline of the Sicilian, Nimzowitch-Rossolimo attack, the black queen moved forward on the queen side. In game 29 the engines exchanged pawns and knights in the center and then the queens were off. Stockfish's eval came down, it gave a pawn and Leela created a passer on the queen side. The game reached a RRB vs RRB position, Leela captured a second pawn yet its eval also came down. Stockfish captured the white passer and Leela captured a pawn and created a passer on the king side. Stockifsh managed to get one pawn back, Leela found no way to improve and the engines shuffled. On move 83 Stockfish captured another pawn, the game was adjudicated on move 103 after exchanging a pair of rooks. In game 30 Leela drove the white queen away and avoided an early queen exchange. The black king moved without castling, Leela captured a pawn and now Stockfish avoided exchanging queens. Stockfish regained the pawn, its queen moved forward and cleared the black queen side pawns. Leela captured a pawn back but Stockfish was still two pawns up with passers on the queen side, yet evals continued to come down. The black rooks kept an eye on the white passers, the engines exchanged a pair of rooks and that doubled the passers. Leela got a pawn back, the game reached a RB vs RB position and was adjudicated despite Stockfish being two pawns up again.
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