After 54 games Stockfish is leading 9-3 with 42 draws. Draw rate is going up again at 78%. Houdini is playing well, but with more than half the match over it's quite clear that Stockfish is better at finding wins. Stockfish will win the match, Houdini needs a miracle to recover from 6 games down.
In game 45 Stockfish had an eval advantage out of the opening, a few pieces were exchanged early including the queens, both engines had passers that could be dangerous later. Houdini's bishop was trapped and could only defend pawns.
The evals started to jump when Stockfish sacrificed its passer on the d file. Through the open file Stockfish exchanged all rooks, then it regained the pawn while exchanging the bishops. Only knights remained, and Stockfish was very happy with the position.
Black's c pawn could not be defended in time, and this created a 3 to 1 pawn advantage on the queen side. Stockfish blocked the black passer with its king and Houdini could not stop the white pawns.
In the reverse game Houdini had an eval advantage that grew to about 1, with similar material composition but different pawn structure. Stockfish simplified to a RB vs RB ending with opposite color bishops, and though Houdini was a pawn up it wasn't enough. The endgame was played for almost 90 moves before both engines agreed to a draw. Houdini couldn't find a win with the help af this unbalanced opening.
In game 47 Stockfish had a small eval advantage after the opening. When pieces and pawns started to be exchanged and the position opened the evals dropped to 0. The engines exchanged down to a BN vs BB position with one pawn each, resulting in a draw.
In game 48 the evals reached 0 even faster. By move 27 on RR vs RR remained, both engines had passers but neither engine could get an advantage and the game was adjudicated when the pawns stopped moving.
In game 49 the engines castled in opposite directions, Stockfish started to attack the king side with a pawn storm and the evals started to climb. Houdini reacted by exchanging everything and after move 24 only RB vs RB remained with Stockfish a pawn up and evals at 1. Evals continued to climb for a short while, Stockfish with a passer in the center, but after exchanging rooks the evals dropped back to 0. Houdini regained the pawn and exchanged the bishops to get a draw.
In the reverse game Stockfish reacted to the pawn storm on the king side by a counter attack on the queen side. The evals fell to 0 and the engines gradually exchanged pieces until reaching a QB vs QB position. The game continued for 25 more moves but the draw was never in doubt.
In game 51 after a few piece exchanges the engines kept their remaining pieces behind their pawn lines and started to shuffle. It took almost 100 moves for the game to finally end, after a long shuffle the engines broke the pawn lines and exchanged down to a drawn queen ending.
In game 52 the engines did not form pawn lines. Through an exchange Stockfish created an advanced passer in the center and gave a rook for a bishop to keep it. Evals were close to 0 even when the pawn reached the 2nd rank. Houdini gave the material back and exchanged pieces, capturing the black passer in an opposite color bishops ending, another clear draw. Third drawn opening in a row.
There were almost no exchanges after the opening of game 53, Stockfish maintained an eval advantage as high as 0.7. The position opened a little with a few exchanges, Houdini sacrificed two pawns but the evals fell to 0. After Houdini sacrificed a third pawn the evals started to turn to its favor as it developed a dangerous attack on the white king. Stockfish gave material to stop the attack, exchanging pieces and giving a rook for a knight so that only QBN vs QRB remained. Houdini pressed on getting evals as high as 0.5, but after queens were exchanged Stockfish's king was no longer in danger. The game continued for another 25 moves before a draw was agreed. This is the first time in the match that Houdini had a serious attack playing with the black pieces.
In game 54 Houdini's eval advantage lasted longer. By move 24 it was a pawn up and had two passers, though there were still many pieces on the board and the strength of the passers was not clear yet. The evals gradually decreased as the engines fought for control of the passers. Eventually Stockfish captured one but Houdini held on to the second and it got to the 7th rank. By this time only RRN vs RRB remained and Stockfish's eval was at 0. Houdini was forced to let the passer go and the game ended in a tablebase draw. Houdini played this opening better than Stockfish in both games, still the result is two draws. Four drawn openings in a row.