After 50 games Stockfish leads 10-3 with 37 draws. Stockfish won two more game pairs, one after a rare blunder by Leela. Leela realized it was a blunder immediately in the following move, suggesting it hadn't considered Stockfish's reply - a bit strange. At the half way point Stockfish has a lead of 7, and Leela only won one game pair so far. The opening bias is slowly increasing, we should see more Leela wins but it is safe to sat that Stockfish will win the match easily.
Games 41-42 started with a 4-ply book 1.e4 c5 2. Nc3 b6. In both games the engines transposed into more popular variations of the Sicilian closed opening. In game 41 there was one pawn exchange after the start, Leela castled long and Stockfish kept its king in the center. Starting from move 17 the engines exchanged minor pieces, evals came down and the game reached a QRR vs QRR position. The engines continued to trade pawns and a pair of rooks, the game was adjudicated a few moves later. In game 42 again Stockfish castled long and Leela did not castle its king. Stockfish gave a bishop for two pawns, it forced the black king to move and opened the h file. Evals came down as the engines exchanged queens and a pair of rooks, Stockfish attacked the back rank with its remaining rook. The engines exchanged rooks and only minors remained, exchanges continued until only B vs BN remained. Stockfish captured all the black pawns, it was 4 pawns up when the game was adjudicated.
Games 43-44 started with a 26-ply book in the Sicilian Dragon, Yugoslav attack, that was played in high level human chess (including a Karpov-Kortschnoi game from 1974). Up to a transposition the games repeated for 21 more plys, white pushed pawns on the king side and black kept the files closed, most pieces were still on the board. In game 43 Leela's evals increased a little, then came back down after Stockfish captured a pawn and reduced to a QRB vs QRN position. The engines traded pawns, evals were low enough for the draw rule. In game 44 played out another long PV agreement after diverging from the reverse game, resulting in a QRB vs QRN position. Evals came down as Leela attacked the white king, they dropped to 0 after the queens were exchanged. The game was adjudicated when enough pawns were exchanged.
Games 45-46 started with an 8-ply book in a rare Queen's pawn game variation. In game 45 Leela weakened the black pawn structure using early exchanges, its eval increased a little. Stockfish pushed a pawn to e4, this restricted the white pieces a little. The engines played out a long PV agreement, the d pawn became a white passer but evals came down. Stockfish gave two pawns to open the king side, then it sacrificed a rook but got it back a few moves later. The game reached a QB vs QN position, Leela was up a pawn but the white king was exposed to checks, evals were close to 0 and the game was adjudicated.
In game 46 Stockfish castled long, the engines mostly agreed in their PV and evals were stable after the start. A minor piece trade opened the g file, Stockfish thought Leela would also castle long but Leela instead chose to capture a free pawn. Stockfish's eval immediately jumped over 3 in a knight sacrifice that surprised Leela.
Leela's eval also jumped (why then make that move??), taking the knight weakened the black e pawn and now the black king was in danger. Stockfish captured two pawns and created two advanced passers. In a series of exchanges Leela captured one passer and reduced to a RRB vs RRN position. material was equal but Stockfish had a protected passer on the 7th rank.
Progress was very slow but evals increased steadily. It took Stockfish 25 moves to capture a pawn on the king side, then exchange a pair of rooks. Leela captured the white passer, but Stockfish reduced to a won B vs pawns ending (Leela could have taken the bishop and lead to a king and pawns ending which was also a white win). Stockfish wins the game pair, it leads 9-3.
Games 47-48 started with a sideline of the Queen's Indian accelerated. In game 47 the engines castled in opposite directions, Leela captured a rook for a knight and evals came down in a series of exchanges. The game reached a QR vs QB position with Stockfish two pawns up, Stockfish captured another pawn but its king was exposed. Leela moved its queen forward and gave checks, evals were low enough for the draw rule.
In game 48 the engines blocked the center, and again castled in opposite directions. There were no exchanges after the start and evals were stable, after a pawn exchange on move 18 the c file opened and Stockfish's eval increased slowly. On move 32 there was another pawn exchange on the king side, all pieces were still on the board.
Leela has to protect the pawns on b5 and g6, and its king was not safe with the g file half open. Evals continued to increase as Stockfish moved all its major pieces to the g file. On move 49 Stockfish pushed the f pawn forward, the first pieces were removed when the engines exchanged a bishop pair. Stockfish opened the g file to attack the black king, and on move 56 it finally went a pawn up.
Leela was busy defending its king and it had to abandon the b5 pawn. Stockfish exchanged all rooks and captured the remaining black pawns. It was 5 pawns up in a BN vs BN position and mated after queening twice. Stockfish wins the game pair, it leads 10-3.
Games 49-50 started with a 14-ply book sideline in the Sicilian closed variation. In game 49 both engines castled and then a pawn exchange opened the f file and both evals jumped a little. The engines exchanged a pair of rooks, then continued to exchange pieces and evals drifted down. Leela was a pawn up in a QRB vs QRB position, evals were close to 0 but the game continued until enough pawns had been exchanged. In game 50 Leela castled and Stockfish kept its king in the center. The engines played out a long PV agreement where Stockfish gave a bishop and then in a long series of exchanges regained the material. The game reached a RRN vs RRB position and evals came down. The engines continued to trade pawns, Stockfish went a pawn up while Leela pushed a passer on the king side. Stockfish captured the passer and exchanged a pair of rooks, the game was adjudicated when evals were low enough.
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