Where did Thompson Falter?

Guided by the annotations in Valeri Beim, Paul Morphy: A Modern Perspective (2005), I made Paul Morphy's tournament games part of the curriculum for many of those students whom I work with one-on-one. Beim's annotations of Morphy's second game against James Thompson seemed to me particularly insightful. Beim draws attention to positional and tactical errors by both players and Morphy's learning process. Despite early missteps, Thompson's drawing chances remained well into the late middlegame or endgame.

Opinions have differed as to where Thompson's fatal error occurred. Of course, today, we seek the truth from our silicon friends. While Geza Maroczy or Beim state that Thompson's game fell apart at a certain point, Stockfish replies, "nah, I can hold that."

We begin after Morphy's 23.Ba3.

Black to move

23...b5

In my quest to go through all of Morphy's games, I am currently reading Geza Maroczy, Paul Morphy: A Collection of his Games with Detailed Notes, trans. Robert Sherwood. Maroczy identifies 23...b5 as the critical error.

Thompson plays all this finely and powerfully, and in fact he can reach a drawn position. At the critical juncture (23rd move), however, he does not find the move that forces equality, and after that the game can no longer be saved. (35)

23...b5 is Stockfish's first choice. ChessBase's cloud shows 1061 visits to this position with 23...b5 as the top choice of Stockfish 18, Stockfish 19, and Fritz 16. Maroczy suggests 23...Bg4, which Stockfish agrees leads to equality.

24.Rfe1 f5

Beim offers, "this terrible blunder decides the game; Black boxes in his bishop when it should be roaming free" (27).

Beim offers 24...Rxe1 25.Rxe1 a5 26.Bd6 (here Stockfish favors 26.b3 Rxa2 27.Bc5 Rd2 28.d6 Be6 29.Rb1 and the game is mostly even with Black ever so slightly better) 26...Rxb2 27.a3 Bh3! 28.Bc7 b4 29.axb4 axb4

White to move

Analysis position from Beim's line

Beim then offers 30.Rd1, which the engine sees as a serious mistake. 30.Ba5 or 30.d6 would be necessary and White is defending a difficult position.

25.f3 Rxe1

25...Ree2 was stronger, according to Beim. Stockfish concurs.

26.Rxe1

Black to move

26...Rd2

26...f4 "might have left him with saving chances", according to Beim. Stockfish concurs that White's advantage is substantially less after 26...f4 than the text move. This move, then, appears to have been Thompson's critical error.

27.d6+-

Beim still finds improvements in Morphy's play after this point. Nonetheless, Morphy's conversion of the advantage through the remainder of this game is of such instructive value that every chess player should dy it. The game continued another 21 moves.