Wednesday, August 4, 2021

Season 21 superfinal games 61-70

After 70 games Stockfish leads 13-5 with 52 draws. Leela won a game pair, but then Stockfish replied with 4 straight game pair wins. Leela clearly blundered in one game, and in another game it realized it was in trouble long after Stockfish's Eval increased. Stockfish's lead is now 8 wins, it is very hard to imagine that Leela can close this gap in the remaining 15 game pairs.

In game 61 Leela went up a pawn, though it was left without pawns in the center. The engines played out a PV agreement, Stockfish castled and Leela kept its king in the center. Evals increased as many pieces were exchanged in the center, including the queens. Only rooks and bishops remained on move 22, Stockfish had a passer in the center while Leela had a pawn majority on the queen side.

 
Evals did not change for a while, the engines traded pawns on the queen side until Leela had one passer left there. Stockfish gave a rook for a bishop and pushed its passer to the 6th rank. Leela managed to capture the passer, and had to give back a rook for a bishop.  On move 41 Leela was two pawns up in a RB vs RB position.


The endgame was very long, Stockfish avoided exchanging pieces and Leela slowly pushed its passer forward. On move 77 Leela captured the black bishop, there was no way to stop the queening and mate followed.

In game 62 both engines castled short, the center remained blocked and the engines opened a file on the queen side. Stockfish had a space advantage and eval over 1.5, but evals did not change a lot. The queen side became blocked, the engines opened a file on the king side. On move 43 only RBN vs RBN remained, the engines mostly shuffled. Stockfish's eval came down, it gave a pawn but couldn't create an attack. The game was adjudicated on move 96. Leela wins the game pair, Stockfish leads 9-5.

In game 63 Leela pushed a pawn to h6, then gave a knight for 3 pawns on the queen side, creating 3 connected passers. Leela castled long, Stockfish kept its king in the center. The game reached a RR vs RRN position on move 29, the king side pawns locked and evals came down. After exchanging a pair of rooks the white king came forward. Stockfish captured a few pawns while Leela created a passer on the king side and pushed it to the 7th rank. Stockfish lost its knight to captured the white pawns on the queen side, the resulting rook ending was a draw.

In game 64 the engines castled in opposite directions, Stockfish pushed pawns on the king side, gave a pawn and opened files near the black king. Leela pushed pawns on the queen side and didn't seem to be worried about its king's safety. Stockfish gave a knight and its eval jumped over 2, then it gave more material and was a rook down. Leela's eval was still low though its king looked very vulnerable.

For a while Stockfish had second thoughts, its eval dropped to 1 and it thought Leela may be all right if it gave its queen for a rook. However Leela had other ideas and Stockfish's eval jumped back up. Stockfish captured a rook and Leela tried to expose the white king with its pawns. On move 37 Leela finally acknowledged it was in trouble and its eval jumped over 5. The white king hid behind doubled black pawns, and a series of exchanged led to a BB vs R ending.

Material seemed balanced but the black king was trapped and the rook could do very little on its own. Stockfish pushed its passer forward and queened, the game ended in mate. Stockfish wins the game pair, it leads 10-5.

In game 65 the engines castled in opposite directions. Stockfish's eval came down quickly, Leela tried to attack on the king side and at one point its eval went over 1, but then quickly came down as well. Leela gave a knight and 3 pawns but it had a passer on the 7th rank. The black king blocked the passer and appeared to be in danger. Stockfish gave the knight back, a quick counter attack allowed it to force a 3-fold repetition draw.

In game 66 there was a similar setup, Stockfish was more patient with its king side attack. Material stayed equal, Leela pushed pawns on the queen side and one reached a3. Stockfish finally opened the king side and on move 37 the pawns there were all gone and the black king was exposed. However, evals were low and the game seemed to be heading for a draw. On move 43 Stockfish's eval jumped over 5 without warning, Leela apparently blundered ?! Stockfish created a central passer and Leela captured a knight, but Leela totally overlooked 44 Rh8+ :

Leela can't play Nxh8 because of d7+ (if c5 then d8=Q+ is check). Leela's eval jumped to 33 (!) after 37 minutes thinking (!!), it had to play Kg7, but then 45. Qc3+ is almost mate. After Re5, 46 Qxe5 Nxe5 47 Rh7+ Leela lost its queen, and the aftermath was a RB vs BN position with white two pawns up and a passer on d6. Stockfish gave the rook for the knight and reduced to a winning bishops ending. Stockfish wins the game pair, it leads 11-5.

In game 67 the engines played out a long PV agreement and opened the queen side. Leela went up a pawn and created a passer on the queen side, but Stockfish's eval came down. The engines continued to exchange pieces and on move 40 the game reached a B vs N ending. Leela wouldn't lower its eval and the engines shuffled, the game was finally adjudicated on move 97.

In game 68 there were only a few exchanges after the start and the queen side stayed closed. The engines started to shuffle on move 23, with pawn moves extending the game. On move 128 (!) Stockfish traded a pawn on the king side, evals were low and Leela's eval even turned slightly negative. Stockfish's eval was not low enough and the shuffling continued. Stockfish's eval started to increase slowly from move 152, it went over 1 and stayed there for a while. The shuffle continued but Stockfish had a long term plan. On move 169 Leela exchanged bishops on the king side, Stockfish moved its pieces there and doubled rooks on the h file. Stockfish's eval jumped over 2 and continued to increase, it waited for the right moment to break the pawn wall with a sacrifice. On move 192, with its eval over 8, Stockfish started the attack.

Stockfish gave two rooks on h6 for a knight, but Leela had to give its queen to avoid mate. The game reached a Q vs RR position, with a passer on g6. Leela had to defend against a back rank mate threat, Stockfish gave a pawn to create a second passer on e6. Leela was nearly paralyzed, the white king came forward and Stockfish started to see mate.

There was no way to prevent Qf7+, reducing to a won king and pawns position. Stockfish wins the game pair, it leads 12-5. Note that the engines had less than a minute on the clock and were in blitz mode for the last 100 moves of the game.

In game 69 there were a few exchanges after the start, the engines concentrated mainly on the queen side. A series of exchanges that started on move 24 cleared all pawns on the queen side, queens were off and Leela was a pawn up. Stockfish's eval gradually came down, the exchanges continued and on move 46 the game reached a knight ending. Leela wouldn't lower its eval, the engines shuffled and the game was adjudicated only on move 82.

In game 70 the beginning was similar, and again the engines concentrated on the queen side. The black queen moved forward and Stockfish's eval went over 1.5 and kept increasing. Leela thought it was perfectly safe, a series of exchanges reduced to a RRB vs RRB position on move 25, Stockfish's eval was over 2.5 already.

Stockfish gave the e pawn and pushed the d pawn to d6. Stockfish's 29th move caught Leela by surprise, it thought almost 9 minutes and its eval jumped over 12. Leela gave its bishop and captured the white passer. Stockfish exchanged a pair of rooks and reduced to a RB vs R position.

Leela was two pawns up with two passers on the queen side, Stockfish kept the black king away and moved its king to block the passers. It then used its piece advantage and the exposed black king to gradually capture black pawns until there were none left. The game ended in a tablebase win. Stockfish wins the game pair, it leads 13-5.


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