After 80 games Stockfish leads 14-8 with 58 draws. Stockfish won 3 game pair wins and it doubles its lead to +6, with only 20 games remaining. It is quite incredible that Leela has not won a game pair since games 23-24, and hard to imagine that Leela can close the gap at this stage.
Games 71-72 started with the Haloween Gambit, with black a knight for a pawn up. In game 71 Leela pushed the pawns in the center to drive the black knights back, then opened a file in the center and the black king moved after check. Leela castled long, Stockfish captured a pawn with its queen and the engines exchanged queens. Stockfish gave the knight back but was two pawns up. Only rooks and bishops remained, evals were still negative but close to 0. The white pieces were more active and the black king was not safe, Stockfish was busy defending despite the material advantage. The engines started to repeat and shuffle and the game was adjudicated. In game 72 the black king didn't move right away, instead the engines exchanged queens early. Stockfish forked king and rook with its knight, leading to a R vs NN imbalance. The engines exchanged pieces and the game reached a RR vs RNN position on move 26. Evals were close to 0, the engines continued to exchange pawns and pieces, Stockfish gave a rook for a knight to create connected passers on the king side. The extra black knight and the white passers canceled out, the game ended in a tablebase draw.
In game 73 both engines castled short despite the fact the the g file was half open, so the white king was partially exposed and the black king could be attacked through the opening. Most action was on the queen side though, by move 18 Leela created a pawn majority there. The engines exchanged most minor pieces and Stockfish's eval dropped to 0. While Leela pushed pawns on the queen side Stockfish maneuvered its knight to h3 and a rook to the g file to trap the white king. Leela saw the problem and waited for a while. When it resumed the pawn march on the queen side Stockfish reduced to a queen ending. Leela had an unstoppable passer, but when it promoted (to a rook, because it didn't matter) Stockifsh had a perpetual check draw.
The g file stayed closed in game 74, both engines castled short and their kings appeared to be safe. There were almost no exchanges after the start, Stockfish pushed pawns on the king side. Leela had two bishops and a knight surrounding its king against a possible attack. On move 21 Stockfish exchanged a pair of pawns on the king side and opened the g file for its rook.
Stockfish's eval started to increase, Leela used the g pawn to remove the white pawn on f5, ans this fully opened the g file. The black pieces tried to cover all squares near the king, Stockfish gave a rook for a knight and took out a crucial defender. The black king was exposed, yet Leela's eval stayed below 1. On move 31 it thought for a long time.
This was the realization moment for Leela, after almost 9 minutes its eval jumped to almost 5. Stockfish's rook joined the attack and the engines started to exchange pieces. The whole point of the attack was that after only NN vs RB remained Stockfish pushed a passer to c7 with the knight on e7 covering the promotion square. Leela was forced to give a rook to stop the pawn, Stockfish had an extra piece and two more pawns to complete the win. Stockfish wins the game pair, its lead is now +4.
Games 75-76 started with engines castling in opposite directions, the center blocked and no exchanges. In game 75 the engines opened the king side but only one pair of pawns was exchanged. After exchanging most minor pieces each engine placed a bishop to close a hole in the pawn line. Stockfish threatened the white king, this kept the white pieces busy defending. The engines started to shuffle, it took Leela a long time to lower its eval for the draw rule.
All pawns stayed on the board in game 76, the engines exchanged most of the minor pieces and formed long pawns lines across the board. The engines shuffled for a while, then Leela doubled rooks on the h file and opened it. Stockfish blocked the entry and the engines started to shuffle. After 30 moves Stockfish's eval jumped over 1, it exchanged a pair of rooks and managed to take control of the open file. Stockfish's eval went down below 1 as the engines started to follow a long PV agreement, then it jumped over 2 again. Probably the limited thinking time caused the eval to be more unstable. Stockfish forced a queen exchange and only RN vs RB remained, still on the PV line.
Stockfish captured the g pawn and its threat on the f pawn forced the black rook to be passive. Leela moved its king back to support the f pawn but it couldn't stay since Stockfish threatened the queen side. Leela traded its f pawn for the white b pawn, this created a king side passer for Stockfish. Stockfish slowly pushed the passer to the 6th rank, Leela's eval started to increase. Stockfish opened the center with a pawn exchange, Leela equalized material and both engines had 2 pawns, all passers. However, evals clearly indicated that Stockfish was winning.
The knight on f6 denied crucial squares from the black rook, while covering the promotion square. Leela tried to block the g pawn with its bishop but Stockfish moved its rook to d7, again supported by the knight. Leela had to give the bishop to stop the pawn, the game was adjudicated 10 moves later. Stockfish wins the game pair, its lead increases to +5.
Games 77-78 started with a 24-ply book in the English symmetrical opening , 3 knights variation. Black was a pawn up and the white king could not castle after moving. In game 77 Stockfish castled early and Leela moved pieces to the king side. On move 18 Stockfish stopped to think for almost 23 minutes, it saw it was in trouble and its eval jumped close to 2. Leela was much stronger on the king side and on move 21 it threatened mate.
Stockfish blocked with the f pawn and then exchanged queens, the danger to the king was gone but Leela had connected passers in the center. Stockfish gave a knight to capture one of the passers, by then both evals were over 3.
Leela had a strong bishop pair, Stockfish exchanged the knight for one of the bishops and captured the e6 pawn. By then Leela had another passer in the center, and the extra piece was enough for a win.
In game 78 Leela did not castle at first, Stockfish created a passer in the center and regained the pawn. Stockfish chose to give away the passer to open a diagonal to the king side, Leela finally castled on move 28 but its king was still vulnerable. Leela exchanged a few pieces and its king moved to the corner, away from the open diagonals. Stockfish's eval increased over 2.
The evals didn't change for a while, Leela captured the two advanced white pawns on the king side while Stockfish cleared the queen side of pawns. Leela had to defend in a wide open position with many pieces, Stockfish is usually better at planning under these conditions. Stockfish's eval started to jump, Leela tried to block the entry points to the back ranks and it was still optimistic according to its eval.
Stockfish alternated its knight and bishop on f5, with the pieces supporting each other. On move 60 Stockfish managed to drive the black king back to the corner and pinned a knight on the back rank. Leela realized it was losing, the game reached a RB vs RN position and was adjudicated before Stockfish captured the knight. There were two white wins in this opening, Stockfish continued to lead +5.
In game 79 Stockfish did not castle its king, there were very few exchanges after the start. The engines opened the h file, the center pawns were locked and only the pawns on the queen side could move. The engines exchanged a pair of rooks and started to shuffle. Leela got nothing out of the open file on the king side, and after 40 moves it tried to open the center and queen side. Stockfish's eval came down, the engines gradually exchanged pieces and only QN vs QB remained on move 73. The game was adjudicated by the draw rule not long afterwards.
In game 80 there were no exchanges after the start, Leela pushed pawns on the queen side and delayed its castling. The engines openes the a file and Stockfish blocked it with a knight. The engines shuffled for a while and Leela castled on move 26. Leela gave a pawn on the queen side on move 39, after some more shuffling the engines started to exchange pawns and Stockfish's eval jumped over 2. On move 58 all pieces were still on the board, Stockfish was a pawn up with a central passer, and the white king looked completely exposed.
Stockfish started to move its king out of the king side. The engines started to exchange pieces and the game reached a QBB vs QBN position on move 71. Leela chased the white king all the way to the queen side, now the black king looked exposed.
Stockfish threatened mate with its queen and g pawn, Leela exchanged one bishop with a knight and eventually lost its bishop to stop the white passer. Stockfish then only had to force a queen exchange while keeping one pawn safe to win. Stockfish wins another game pair, increasing its lead to +6.
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