After 26 games Stockfish leads 6-2 with 18 draws. Game 17 is under review and the officials may change the result to a draw. 5-2 looks a lot better for Houdini than 4-0 did. Can Houdini make a comeback?
Game 21 started with a 7-ply book of the King's Gambit Accepted. As expected evals out of the opening favored black and the fans were anxious to see how Stockfish will handle being a pawn down with a king that can't castle. However, Houdini could not find a line that would improve its position and Stockfish equalized quickly. Unexpectedly, as the game progressed evals started to suggest Stockfish was better.
The advantage seemed to be due to having more space, and it was not clear how to proceed. Evals did not move for a while as the engines shuffled pieces.Then Stockfish made a small hole in Houdini's pawn line on the king side, with evals rising above 1. Stockfish used all its pieces to apply pressure on Houdini's position through the hole.
Still Houdini's position looked solid enough, it wasn't going to fall through a direct attack on the king. Instead Stockfish attacked the center of the board causing a series of exchanges that resulted in a knight for rook trade and a QRB vs QBN position.
Using the rook and queen Stockfish could check the black king and go after the weak black pawns. It took many more moves and was far from easy but Stockfish managed to eliminate the black queen side pawns, and after queens were exchanged its passer was unstoppable. Quite a surprising win for Stockfish. Does this game show that the King's Gambit is good for white?
In the reverse game Stockfish as black had an eval advantage for a longer time and its pieces stayed active. However, it too could not find a winning line and as pieces were being exchanged the evals drifted towards 0. After exchanging queens with only RBN vs RBN left the position became static and a draw was reached. A second good result for white in the King's Gambit, I vote for having more games with this opening in TCEC.
In game 23 Stockfish seemed to sacrifice a rook and then a knight, when in fact the knight could not be taken due to a mate, and a few captures later Stockfish got the material back. It was a pawn up with evals above 1 in a QBN vs QBN position from move 28. After exchanging queens Houdini created an advanced passer, but it couldn't hold it after bishops were exchanged as well. The remaining knight ending was a draw but it took almost 50 moves for the engines to realize this.
The reverse game 24 took a different path. Houdini had a supported advanced passer in the center and Stockfish had a 3 to 1 pawn advantage on the queen side. Houdini's eval was above 1 but it did not increase, Houdini couldn't improve its pawns position. Stockfish created two passers on the queen side, one of them advanced. When the king side pawns became static both engines started to shuffle and the evals started to go down. With evals close to 0 the ending was spectacular, Stockfish sacrificed a bishop to eliminate the white pawns, then with queening threats and an attack on the white king got the material back and reached a drawn RB vs R ending.
Houdini's king remained uncastled in game 25 but Stockfish was not able to get a useful advantage. Evals were at 0 from move 27 even though Stockfish had a bishop pair and a passer. The game reached a RB vs RB ending which led to a drawn tablebase position.
Game 26 was nothing like game 25. Both engines castled quickly and there were many exchanges after the opening. After queens were exchanged Houdini had an eval advantage, with better pawns on the queen side.
Here Stockfish chose to take the d pawn and abandon its a pawn. This looked dangerous because Houdini's b pawn became a passer. After some simplification only RB vs RB were left. Did Stockfish have the power to stop the passer?
Stockfish saw it was in trouble, evals jumping high. Houdini took longer to realize it was winning, it managed to queen the pawn for the price of a bishop, forcing Stockfish to lose its rook and reaching a won R vs B ending. Houdini's second win, it is not going down without a fight.