Surprising Stockfish blunder at CCC

[Jouni]

[d]5k2/6p1/4P1p1/2R3n1/2BKp3/2r5/5P2/8 b - - 0 41

SF plays 41. -Rd3+ losing against Integral!

[Ajedrecista]

Hello Jouni:

A brief analysis suggest that 41.- ..., Rxc4+ is the best move by black, with around +1 evals. After some captures, not all of them forced, for example, 42.- Rxc4, Nxe6+; 43.- Kxe4, I get around +0.8 evals with Multi-PV = 7 and tons of TB hits to the full set of 3, 4 and 5 Syzygy EGTB. Nevertheless, this is a 7-man losing endgame according to the Syzygy site, so it could be that the posted position was already losing. Any thoughts?

Regards from Spain.

Ajedrecista.

[peter]

A brief analysis suggest that 41.- ..., Rxc4+ is the best move by black, with around +1 evals. After some captures, not all of them forced, for example, 42.- Rxc4, Nxe6+; 43.- Kxe4, I get around +0.8 evals with Multi-PV = 7 and tons of TB hits to the full set of 3, 4 and 5 Syzygy EGTB. Nevertheless, this is a 7-man losing endgame according to the Syzygy site, so it could be that the posted position was already losing. Any thoughts?

SF dev. with 6men Syzygys, 30 threads of 16x3.5GHz and 32G hash after some Forward- Backward

[d]5k2/6p1/4P1p1/2R3n1/2BKp3/2r5/5P2/8 b - - 0 1

Analysis by Stockfish dev-20241222-f656fdfa:

41...Txc4+ 42.Txc4 Sxe6+ 43.Kxe4 Kf7 44.Ke5 Sg5 45.Tc7+ Kg8 46.f4 Sf3+ 47.Kd5 Sh2 48.Ke6 Sg4 49.Tc8+ Kh7 50.Ta8 Sh6 51.Ke5 Sf7+ 52.Kd5 Sh6 53.Tf8 Sg4 54.Ke4 Sh6 55.Kf3 Sg8 56.Kg4 Sf6+ 57.Kg5 Se4+ 58.Kh4 Sf6 59.Td8 Se4 60.Td4 Sc5 61.Td6 Se4 62.Te6 Sc5 63.Te8 Sd3 64.Kg5 Sc5 65.Te3 Sd7 66.Th3+ Kg8 67.Kxg6 Sf8+ 68.Kf5 Kf7 69.Ta3 Kg8 70.Ta7 Sh7 71.Ke5 Sf6 72.f5 Sh5 73.Ke6 Sf4+ 74.Ke7 Sd5+ 75.Kd6 Sf4 76.Ta4 Sh5 77.Ke6 Sf6 78.Ta1 Sh5 79.Ta8+ Kh7 80.Kf7 Sf6 81.Ta4 Sg8 82.Th4+ Sh6+ 83.Ke6 Kg8 84.Txh6 gxh6 85.Ke7 Kg7 86.f6+ Kg8 87.f7+ Kg7 88.f8D+ Kg6 89.Df6+ Kh5 90.Dg7 Kh4 91.Dxh6+ Kg3 92.Dd2 Kf3 93.De1 Kg4 94.De3 Kf5 95.Kf7 Kg4 96.Kg6 Kh4 97.Kf5 Kh5 98.Dh3#
Tiefe: 82/92 00:02:08 3711MN, tb=51637519
+- (199.48)

[Jouni]

So blunder was earlier in game. Whole game
[pgn][Event "CCC24 Blitz: Semifinals (3|2)"]
[Site "?"]
[Date "2025.01.08"]
[Round "1"]
[White "Integral"]
[Black "Stockfish"]
[Result "1-0"]
[ECO "C41"]
[GameDuration "00:09:09"]
[GameEndTime "2025-01-08T09:10:40.832 PST"]
[GameStartTime "2025-01-08T09:01:31.239 PST"]
[Opening "Philidor's defense"]
[PlyCount "119"]
[TimeControl "180+2"]
[Link "https://www.chess.com/computer-chess-ch ... ls&game=50"]

1. e4 e5 2. Nf3 d6 3. Bc4 Bg4 4. h3 Bh5 5. d3 Nd7 6. Be3 Ngf6 7. Nbd2 c6 8. Bb3
b5 9. a4 a6 10. g4 Bg6 11. Nh4 d5 12. exd5 Nxd5 13. Nxg6 hxg6 14. Qf3 Nc5 15.
Bxc5 Bxc5 16. h4 Bb4 17. c3 Be7 18. Kf1 Kf8 19. g5 Nf4 20. d4 f6 21. Ne4 bxa4
22. Bc4 Rb8 23. h5 Rxh5 24. Rxh5 Nxh5 25. dxe5 f5 26. Nc5 Bxc5 27. Qxc6 Nf4 28.
Qxc5+ Qe7 29. Qd4 Qb7 30. Ke1 Qh1+ 31. Bf1 Qe4+ 32. Qxe4 fxe4 33. Ra2 a5 34. Kd2
Ne6 35. Ke3 Nxg5 36. Rxa4 Rxb2 37. Rxa5 Rb3 38. Rc5 Rb1 39. Bc4 Rc1 40. e6 Rxc3+
41. Kd4 Rd3+ 42. Ke5 Rd2 43. Rc8+ Ke7 44. Rc7+ Kd8 45. e7+ Kxc7 46. e8=Q Rd7 47.
Bb5 Rf7 48. Qc6+ Kb8 49. Qd6+ Rc7 50. Qd8+ Kb7 51. Ba6+ Kb6 52. Kd5 Nf3 53. Qd6+
Ka5 54. Qxc7+ Kb4 55. Qc1 Ka4 56. Bc4 Nd4 57. Kxd4 Kb4 58. Qc3+ Ka4 59. Qb3+ Ka5
60. Qb5# 1-0[/pgn]