2

This is a game from the TCEC Season 18 superfinal, which Leela won with a beautiful positional bind.

[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
[Event "TCEC Season 18 - Superfinal"]
[Site "https://tcec-chess.com"]
[Date "2020.06.27"]
[Round "65.1"]
[White "LCZero v0.25.1-svjio-t60-3972-mlh"]
[Black "Stockfish 202006170741"]
[Result "1-0"]
[Annotator "archive"]

1. d4 Nf6 2. c4 e6 3. Nf3 Bb4+ 4. Nbd2 O-O 5. a3 Be7 6. e4 d5 7. e5 Nfd7 8. Bd3 c5 9. h4 g6 10. O-O Nc6 11. Nb3 Bxh4 12. Bh6 Re8 13. Re1 cxd4 14. Qc2 dxc4 15. Bxc4 Nb6 16. Rad1 Bd7 17. Nc5 Rc8 18. b4 Nxc4 19. Qxc4 Be7 20. Ne4 Nxb4 21. Qxb4 Bxb4 22. axb4 f5 23. Nf6+ Kh8 24. Rxd4 Rc7 25. Red1 Re7 26. b5 b6 27. Kh2 Rb7 28. Ng5 Qc8 29. R1d2 Rc7 30. Rd6 Rb7 31. R2d4 Rc7 32. Rd1 Rb7 33. R6d4 Rc7 34. f4 Rb7 35. Nxe6 Rxe6 36. Nxd7 Kg8 37. Nf6+ Kf7 38. Rd8 Qc5 39. Nxh7 Re8 40. e6+ Rxe6 41. Ng5+ Kf6 42. Rf8+ Qxf8 43. Bxf8 Rc7 44. Rd4 Rb7 45. Kg3 Rc7 46. Rd3 Rb7 47. Kh4 Rc7 48. Kg3 Rc4 49. Rd7 Re3+ 50. Kf2 Rxf4+ 51. Kxe3 Ra4 52. Be7+ Ke5 53. Kf3

Link to the game from the TCEC archives if one wants to see the engine evals and PVs.

Where did Stockfish go wrong? Stockfish knew it was lost after 22. axb4, so the critical error must have happened before this. Leela didn't like 20...Nxb4, but the analysis by GM Matthew Sadler is that White has a pleasant advantage anyway after that line. Meanwhile newer versions of Stockfish with NNUE enabled don't seem to think 20...Nxb4 is a mistake either. In the position after 20. Ne4, the version of Stockfish on Lichess (Stockfish 13+ NNUE) at depth 33 thinks 20...Nxb4 is the best move with +0.1 eval; the next-best move is 20...a5 with +1.3 eval.

Playing through the game with Stockfish 13+ NNUE, it's clear that somewhere around move 20, it is missing some critical game-winning line, but it's not clear how to avoid that line and the losing move is. Can anyone tell?

2

There is no one particular mistake. It is white building the attack around black king 7.e5 ... 12 Bh6 and finally deadly 23 Nf6

They are playing somewhat imprecise in some segments around 20. so it is more of a "who made a worse choice" than about one particular error. Not that they are playing wrong, it is in the sense of position being complicated enough to exactly name all details in it.

However, the basic error that allows the attack build-up is 9. ... g6? (h6 is better). This move is just calling for an attack.

Before that, you can take as an imprecision: black castled too early and then played 6 ... d5 forcing the only figure that is defending the king side, a knight, out of the game.

The rest is just an execution. Notice as well how useless black rooks are after 24. Covering nothing, defending a poor locked bishop. It is a disaster in making.

Sometimes people think that chess is about one mistake you make. No. Many times it is a small connected chain of poor decisions that just created a momentum, a combination, and when that starts, like here, if you know what you are doing, there is really no defense.

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