There are tons of questions about the longest forced mate on here and other chess forums. Usually the answers are the 2 Knights forced mate and another one that evidently takes 549 optimal moves. Ultimately those discussions often devolve into debate about the 50 move rule.

However as a novice player it often boggles my mind when, in real games, players are able to recognize unavoidable checkmate on a non-empty board dozens of moves in advance. Hence, what I am wondering about is: what is the longest forced mate optimally played in documented competition? In other words, in competitive play (international, national, league, etc.), what comes to mind as the furthest time (in moves) from checkmate when resistance is futile? Something a la "that's mate in 15."

Edit: I imagine that this situation usually brings about resignation, so I should clarify that I'm not interested in if it was ever played out, but rather what the maximum number of moves was in advance of checkmate when this futility was ensured.

  • People resign when the position is "lost", but that doesn't mean there is a forced checkmate. It could just mean they are down enough material. I guess you could say mate is "unavoidable in dozens of moves" when you are down a piece, but that doesn't mean anyone can calculate how! The notion that anyone, even grandmasters, calculates dozens of moves in advance is a myth. Also, if you find a position from a real game that can be proven to be, say, mate in 20, that doesn't mean that either of the players noticed. – itub Jan 20 '18 at 22:21
  • @itub: Interesting point; I hadn't realized that. The top players must at the least have profound recall of many permutations of moves given a number of scenarios. Perhaps it's just having played and studied so many games, almost any position is recognizable. – marcman Jan 21 '18 at 5:18
  • It is not that almost any position is recognized but that it likely falls into a recognizable category. – DanielWainfleet Jan 24 '18 at 7:00

To present a starting point, there is mate in 10 in the famous Steinitz-von Bardeleben game. Black stormed off after 25. Rxh7+, from which point it is mate in 10:

[FEN ""]
[StartPly "49"]

1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.c3 Nf6 5.d4 exd4 6. cxd4 Bb4+ 7. Nc3 d5 8.exd5 Nxd5 9.O-O Be6 10.Bg5 Be7 11.Bxd5 Bxd5 12.Nxd5 Qxd5 13.Bxe7 Nxe7 14.Re1 f6 15.Qe2 Qd7 16.Rac1 c6 17.d5 cxd5 18.Nd4 Kf7 19.Ne6 Rhc8 20.Qg4 g6 21.Ng5+ Ke8 22.Rxe7+ Kf8 23.Rf7+ Kg8 24.Rg7+ Kh8 25.Rxh7+ 1-0 (25...Kg8 26. Rg7+ Kh8 27. Qh4+ Kxg7 28. Qh7+ Kf8 29. Qh8+ Ke7 30. Qg7+ Ke8 31. Qg8+ Ke7 32. Qf7+ Kd8 33. Qf8+ Qe8 34. Nf7+ Kd7 35. Qd6#)
  • I have to say I don't see why black doesn't play Qxe7 in move 22. There's doesn't appear to be any risk of getting pinned by the white rook. I'm also not seeing why white subsequently doesn't play Rxd7 or Qxd7 in move 23. And again in move 24, black doesn't play Qxg7 which would seem to remove the threat of white's bishop. Clearly these guys were many levels beyond.... – marcman Jan 20 '18 at 21:01
  • @marcman: 22...Qxe7 23. Rxc8+ Rxc8 24. Qxc8+ Qd8 25. Qxd8+ Kxc8 leaves white up a knight. – user1108 Jan 20 '18 at 21:29
  • There's no mate in 10, or any forced mate for that matter as far as I could find using Stockfish. The mate can be "averted by ruinous loss of material" like the chessgames.com page says. Of course, the position is still lost. Maybe there is a forced game in 18 or so... – itub Jan 20 '18 at 22:03
  • If 26..., Kt8 27. Nh7+ – DanielWainfleet Jan 24 '18 at 7:06

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