After 20 games Stockfish leads 5-2 with 13 draws. Leela won a game pair, where in game 12 Stockfish only drew and the game ended in fortress almost identical to the one in game 8. Stockfish immediately won a game pair, then there were two double draws. In game 19 Leela couldn't find a win despite having a high eval. Stockfish won the reverse to increase the gap to 3 wins. So far the match is closer that what was expected after the premier division.
Games 11-12 started with a 20-ply sideline in the French Winawer, advance variation. In game 11 there were a few pawn and minor piece exchanges in the center and Stockfish went a pawn up. The black king moved without castling, Stockfish pushed the d pawn forward and created a passer. Evals were stable above 1, the black king side rook moved forward and offered it for a bishop (LS) but Leela didn't take. Leela regained the pawn and its eval started to increase. Leela then captured the black passer and Stockfish's eval also started to increase.
The engines played out a very long PV agreement and evals continued to increase. Stockfish gave the king side rook for the other (DS) bishop and regained the pawn. Stockfish captured another pawn while Leela moved a rook to the back rank through the open d file. Leela captured a pawn and exchanged a pair of rooks. The game reached a QRB vs QBN position and the engines cleared the queen side pawns.
Leela's progress was slow, it pushed the h pawn and it became a passer. Then Leela exchanged queens and moved the rook to the 7th rank. The white king moved forward and Leela created another passer, Stockfish lost more material and was mated.
In game 12 after the initial exchanges in the center Leela was up a pawn as before, this time the engines played out a long PV agreement that involved a RN for Q trade. Stockfish's eval started to increase but dropped back in the middle of the PV agreement, what did it see? Leela moved a rook to h7 to protect the g7 pawn, an awkward square for the rook. However, Leela just played waiting moves and Stockfish couldn't find a way to improve. It forced Leela to move the g pawn to avoid mate, but nothing else. After a long shuffle Stockfish pushed pawns on the king side and its eval increased for a few moves but then came back down. It opened the g file and exchanged a pair of rooks, the game reached a Q vs R position and ended in a fortress almost identical to the one in game 8. Leela wins the game pair, Stockfish leads 3-2.
Games 13-14 started with a 24-ply sideline of the KID orthodox varation played in high level human chess. In game 13 Leela pushed pawns on the queen side, the engines exchanged a pair of pawns on the king side. For a few moves Leela's eval increased a little, then came back down. Stockifsh opened the g file and threatened the white king, the first piece exchange was on move 34. Leela had a bishop pair advantage but evals came down. After exchanging queens Stockfish captured two pawns, then traded a rook for one of the bishops. The game was adjudicated 10 moves later.
In game 14 the engines repeated the first 13 plys of game 13. Leela moved its queen forward on the king side, too soon perhaps, and evals started to increase. Stockfish exchanged pawns on the queen side, opening files there. On move 35 the first minor pieces were exchanged, both engines had a passer on the queen side but Stockfish's passer was on d6 supported by major pieces.
Leela blocked the white passer and protected its own with knights, it didn't try to attack the white pawn. The engines exchanged pieces until the game reached a RB vs RN position. Stockfish saw a win in its PV.
Leela lost the knight for the white passer, Stockfish captured the black passer and the game ended in a tablebase win. Stockfish wins the game pair, it leads 4-2.
Games 15-16 started with a sideline of the Old Indian defense, Tartakower variation. In game 15 the engines exchanged minor pieces and castled in opposite directions. The c file was opened and the engines exchanged a pair of rooks. Stockfish pushed pawns on the queen side and captured a pawn on the king side, creating a passer. The engines played out a long PV, exchanging the remaining rooks and more pieces and pawns. The game reached a BN vs NN position with white a pawn up, Stockifsh's eval was 0 and Leela lowered its eval slowly. Leela blocked the black passer on the 2nd rank, the game was adjudicated on move 86. In game 16 there were only a few exchanges after the start, a minor piece exchange and a pawn exchange in the center. Both engines castled short and developed pieces behind their pawn lines, on move 25 a pawn exchange opened the a file. Leela's eval came down, it moved a rook forward and exchanged a pair of rooks. Stockfish created a passer on the queen side and pushed it to the 7th rank, its eval also came down. The game reached a RBB vs RBN position and Leela captured the passer. There were too many pieces for the draw rule and the game ended in repetition.
Games 17-18 started with a 22-ply line in the Sicilian Dragon, Yugoslav attack, popular in high level human chess. There was one pawn exchange and all pieces were on the board, the engines castled in opposite directions. In game 17 the engines quickly left theory, there was a minor piece exchange on the queen side and Leela pushed pawns on the king side. In a series of exchanges the d file was opened and a pair of rooks was exchanged, Leela went a pawn up but evals came down. The game reached a RB vs RB position, Stockfish regained the pawn and the game was adjudicated. In game 18 the engines also left theory and exchanged queens early, there were no pawn exchanges after the start and the engines slowly exchanged minor pieces. The first pawn exchange opened the g file on move 36, the game reached a RRB vs RRN position and evals came down. After exchanging a pair of rooks the game was adjudicated.
Games 19-20 started with the Modern defense, Averbach system. In game 19 the engines locked the center and opened the c file. Evals increased steadily, a few minor pieces were exchanged. Leela pushed pawns on the king side and doubled rooks on the c file. The kind side was also locked and all pieces moved to the queen side.
Leela's eval was close to 4 but from here on it gradually came down. Stockfish exchanged knight for bishop and Leela couldn't find a safe way to penetrate the pawn wall. On move 62 Stockfish gave a pawn and the a file opened, but the white pieces couldn't force their way through. The engines shuffled for a long time, on move 99 they exchanged a pair of rooks, on move 120 the remaining rooks were gone. Leela gave a bishop for pawns to break the pawn wall but evals were close to 0 and the game was adjudicated.
In game 20 the first few moves repeated game 19 with the locked center and open c file. Leela chose to exchange pawns on the king side and Stockfish's eval started to increase. There was a series of exchanges where Leela captured a pawn and both engines created advanced passers in the center. The black passer was unsupported and Stockfish captured it.
Stockfish gave a bishop and captured a rook for the passer. Leela tried to attack the white king but was not strong enough. The game reached a QRN vs QBN position, each engine had a passer.
Stockfish's progress was very slow, it let Leela capture the f passer as it thought how to break the bishop-pawn pair blocking the center. The bishop moved but was still a strong piece in the center. Stockfish managed to move the queen forward while keeping its king safe, on move 68 it finally exchanged knight for bishop. Stockfish pushed the h pawn and captured the black knight, the game ended a move before mate. Stockfish wins the game pair, it leads 5-2.
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