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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.

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  • 1
    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
    Commented Jan 20, 2018 at 22:21
  • 1
    @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
    Commented Jan 21, 2018 at 5:18
  • 1
    It is not that almost any position is recognized but that it likely falls into a recognizable category. Commented Jan 24, 2018 at 7:00

4 Answers 4

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I discovered a game from a few weeks ago that features a forced mate in 13 moves that was administered OTB. The game in question is Dubov-Svane, and the claim came from Agadmator’s analysis, for which engine analysis yielded his claim correct.

Although Black made a move to try and trick White in the real game, shortening the sequence, in my eyes, it still qualifies as a forced mate in 13 moves.

What Black "should" have played, in terms of engine analysis that is, is included as a sideline.

[Title "Daniil Dubov-Rasmus Svane. European Team Championship, Batumi Georgia, 10/31/19"]
[FEN ""]
[startply "58"]

1. c4 e6 2. Nc3 d5 3. d4 Nf6 4. Nf3 Be7 5. Bf4 O-O 6. e3 b6 7. Qc2 Ba6 8. O-O-O dxc4 9. Ng5 Nc6 10. a3 g6 11. h4 Bd6 12. g3 Qe7 13. h5 e5 14. hxg6 hxg6 15. Bg2 exf4 16. Bxc6 fxg3 17. Kb1 Rad8 18. f4 Bc8 19. Rde1 Kg7 20. Nd5 Nxd5 21. Rh7+ Kg8 22. Rxf7 Rxf7 23. Qxg6+ Kf8 24. Qh6+ Rg7 25. Bxd5 Ke8 26. Qh5+ Kd7 27. Qh3+ Ke8 28. Qh5+ Kd7 29. Be6+ Kc6 30. Qf3+ Kb5 31. Bxc4+ Ka5 32. Qd5+ Bc5 33. b4+ Ka4 34. Qg2 (34... Bf5+ 35. Ka2 Rd5 36. Qxd5 Qd7 37. Qb7 a5 38. Ne4 Bxd4 39. exd4 Bxe4 40. Qxe4 Qf5 41. Qxf5 axb4 42. Bb3#) Bxb4 35. Qc6+ Kxa3 36. Bb3 Bd7 37. Qc1+ Kxb3 38. Qc2+ Ka3 39. Qa2#
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    34 . . . Bxb4 is not necessarily a mistake: it forced White to find 36 Bb3! to win, while after Bf5+ 35 Ka2 Rd5 36 Qxd5 the win is routine even if it takes a few moves longer to reach checkmate. Commented Jun 28, 2022 at 21:13
5

To present a starting point, there is a mate in 10 in the famous Steinitz-von Bardeleben game. Bardeleben quietly walked away after 25. Rxh7+.

[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#)
4
  • 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
    Commented Jan 20, 2018 at 21:01
  • @marcman: 22...Qxe7 23. Rxc8+ Rxc8 24. Qxc8+ Qd8 25. Qxd8+ Kxc8 leaves white up a knight.
    – user1108
    Commented Jan 20, 2018 at 21:29
  • 3
    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
    Commented Jan 20, 2018 at 22:03
  • If 26..., Kt8 27. Nh7+ Commented Jan 24, 2018 at 7:06
4

Wikipedia's article on the KBN/K checkmate cites a blindfold game(!) between grandmasters (L. Ljubojević and J. Polgár)[https://www.chessgames.com/perl/chessgame?gid=1092636] at 1994 Amber Chess Tournament. Polgár won by checkmate, and the last ten moves were played correctly by both players (the last "error" was 96...Ke4-e3, when Bd1-f3 would have mated a move faster according to the "tablebase"):

[Title "L. Ljubojević vs. J. Polgár, 1994 Amber Chess Tournament (blindfold)"]
[FEN ""]
[startply "192"]

1. e4 c5 2. c3 d6 3. d4 Nf6 4. Bd3 g6 5. h3 Bg7 6. Nf3 O-O 7. O-O Qc7 8. Qe2 a6 9. Bf4 b5 10. e5 Nd5 11. Bg3 Qb6 12. Nbd2 cxd4 13. cxd4 Nb4 14. Be4 d5 15. Bb1 a5 16. Nb3 a4 17. Nc5 N8c6 18. Qe3 Na5 19. Bf4 Nc4 20. Qc3 Nc6 21. a3 f6 22. exf6 Rxf6 23. Bg5 Rf7 24. Be3 Rxf3 25. gxf3 e5 26. dxe5 Bxe5 27. Nd3 d4 28. Nxe5 N4xe5 29. Ba2+ Kg7 30. Bd5 Ra6 31. f4 Nc4 32. Bxc6 dxc3 33. Bxb6 Rxb6 34. Bxb5 Rxb5 35. bxc3 Bxh3 36. Rfd1 Rb3 37. Rd4 Rxc3 38. Rad1 Bf5 39. Re1 Nb2 40. Re3 Rxe3 41. fxe3 Be6 42. e4 Bb3 43. Rd7+ Kf6 44. Rxh7 Nc4 45. e5+ Ke6 46. Rg7 Bc2 47. Rc7 Nxa3 48. Rc3 Bb3 49. Rc6+ Kf7 50. Rc7+ Kf8 51. Rc6 Kg7 52. Rc7+ Kh6 53. Rc6 Kg7 54. Rc7+ Kf8 55. Rc6 Bf7 56. Ra6 Be8 57. Ra7 Nc2 58. Kf2 a3 59. Ke2 Nd4+ 60. Kd2 Nb5 61. Ra6 Ke7 62. e6 Nd6 63. Kc2 Nc4 64. Kc3 Bb5 65. Ra7+ Kxe6 66. Kb4 Nd6 67. Rxa3 Be8 68. Ra5 Nb5 69. Kc5 Kf5 70. Ra8 Nc7 71. Rc8 Ne6+ 72. Kd6 Ba4 73. Ra8 Bd1 74. Ra5+ Kf6 75. Ra1 Be2 76. Ra4 Bd1 77. Re4 Ng7 78. Re1 Bf3 79. Rf1 Be4 80. Re1 Kf5 81. Ke7 Nh5 82. Rg1 Nxf4 83. Rxg6 Nxg6+ 84. Kd6 Kf6 85. Kc5 Ke5 86. Kc4 Bd5+ 87. Kd3 Nf4+ 88. Ke3 Be4 89. Kd2 Kd4 90. Kc1 Kc3 91. Kd1 Bc2+ 92. Ke1 Kd3 93. Kf2 Ke4 94. Kg3 Bd1 95. Kf2 Nd3+ 96. Kg3 Ke3 97. Kh4 Kf4 98. Kh3 Ne1 99. Kh4 Ng2+ 100. Kh3 Kf3 101. Kh2 Kf2 102. Kh3 Be2 103. Kh2 Bg4 104. Kh1 Ne3 105. Kh2 Nf1+ 106. Kh1 Bf3#
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I'm afraid OP's assumptions are not correct. Its' not that we see, like, 10 move mate patterns. That's nonsense. Those are calculated. And it takes time. Sometimes ten minutes, sometimes 40 minutes! Nobody calculates dozens of moves ahead either. It's total nonsense too. There are forced positions, yes. In such positions sometimes 20 moves ahead can be calculated if these are forced positions, e.g., with mate threats, or material loss. Again, OP's assumptions are inaccurate as to these positions being totally forced. They are not, especially long ones. Even short ones are usually not absolutely forced. However, they are forced in a way that material can be lost, which means certain moves need to be played, otherwise (if material is lost) you can resign on the spot. However, it's not like mate is coming right away. No, that's incorrect. It's the other way round. The defensive side has to hold on to the material no matter what (or it's resignable on the spot - nobody is going to play a piece down other things being equal at high level) which creates kind of forced lines to calculate. As I said, such lines can be 20 moves deep and even more. Here's a situation like that from a real game but it's not something too unusual or especially weird. It's not the longest sequence either but it's 18 moves long and it ends with a mate (White's to move):

[fen "r1b3nr/pp1p1k1p/4ppp1/q2Nb3/8/1B6/PP3PPP/R1BQR1K1 w - - 0 1"]


1. Rxe5 fxe5 2. Qf3+ Ke8 (2... Kg7 3. Bh6+ Nxh6 ( 3... Kxh6 4. Qf8+ Kg5 5. g3 Qd2 6. h4+ Kg4 7. Kg2 Kh5 8. Kh3+-) 4. Qf6+ Kg8 5. Ne7#) 3. Bh6 Nxh6 4. Qf6 Ng8 ( 4... exd5 5. Qxh8+ Ke7 6. Qxe5+ Kf8 7. Re1 Qd2 8. Qe8+ Kg7 9. Re7+ Kf6 10. h4 Qc1+ 11. Re1+-) 5. Qxh8 Kf7 6. Qxh7+ Kf8 7. Bc2 Qxd5 8. Bxg6 Nh6 9. Qxh6+ Ke7 10. Qg7+ Kd6 11. Qf8+ Kc6 12. Rc1+ Kb5 13. a4+ Ka6 (13... Kxa4 14. Qa3+ Kb5 15. Bd3+ +-) 14. Qb4 Qa5 15. Bd3+ b5 16. axb5+ Kb6 17. Qd6+ Kb7 18. Be4#  

White had to calculate 18 moves ahead here till mate. Of course, an engine will see right off the bat that Black's losing and will focus only on prolonging the game. Humans don't play like that. As I said it is as good as resigning on the spot. What good is it prolonging the game if you consider it dead lost and await only a mate? So, Black held on as hard as it could to stay in the game. However White had calculated 18 moves ahead till mate and won this game. This game is a puzzle now for highly professional players. It's extremely forcing. Yet, it's not absolutely forcing like the OP wanted. Absolutely forcing very long lines can be found in artificial made-up puzzles or they can be generated by the computer. Made-up puzzles are often absolutely forcing, e.g., mate in 8, 12 or 16 moves.

The forced mating position is not absolutely forced but Black may lose material or continue to hang on at the risk of being mated. This is not the longest example the OP wanted (longer and more complicated forced examples from real games exist I can assure you). It's a clarification of misunderstanding. The above diagram is a mere example of a forced play with almost all moves being checks hardly leaving any leeway for Black. That's why it is short in terms of branching out with most subvariations leading to Black's fast demise and hence, they are dismissed out of hand (even if they protract the game beyond 25 moves). The engine will play it as if it's all calculated and opponent has, like, Elo 3500, and since it's dead lost the engine will seek only to prolong the game and will happily give away material and whatever just to receive mate later. Even in the dumbest situation when a mate is looming four moves ahead, the engine will sacrifice pieces checking your king, e.g, checking your king with a Queen so that you capture said Queen to drag the situation by one more move. Humans could not care less about such things. Humans aren't going to give away material with other things being equal if there's a chance to fight off the attack and bring the king to safety.

What's more, I don't really know if the player calculated all 18 moves (he probably did) in the diagram above but that's irrelevant because this line is pretty forcing anyway. It means it is not that difficult for a professional to calculate it through in 20-30 minutes.

Bottom line: if the sequence is as long as 20 moves, human analysis is going to be imperfect or it's going to be a made-up puzzle because such puzzles can be absolutely forcing and long. Real game positions are usually not 100% forcing, especially if they are long. Actually a human can also drag the game out. In the diagram above if Black had been told to drag out the game and make sure not to get mated in 25 moves no matter the cost, even at the expense of the Queen, I'm sure Black would have succeeded with the task. But to what end? To make sure the game is really lost but not too fast? Point being, White could have slipped up if the above 18 moves had not been thought out well enough. Black bravely tried every trick in the book to bring the king to a safe haven and keep a relative material parity. But if Black had lost a piece while bringing its king to safety, the game would have been completely lost even with a slight inaccuracy from White. However, if some inaccuracy had been made in the calculation of 18 moves above, Black might have drawn.

Now then, something like mating with a knight and bishop is perceived as forcing but it is not something we calculate with any great depth. That's because the losing side has too many moves, and it's too much of branching out to be calculated. Yet, it's an easy win by following an algorithm, a recipe like a stepladder mate. It's just a more advanced recipe. It's wackiness to think mating with a knight and bishop is some forcing calculation that a player made at some ridiculously long depth of 25 moves ahead. It's never like that. Only computers calculate like that and only when they don't have the endgame tablebase. If they have it, they just retrieve ready solutions. And if I made 10-15 moves exactly perfect according to engine or tablebase while mating with a bishop and knight, it doesn't mean I was calculating 10-15 moves ahead. No, it was just a coincidence. It means I was simply using the technique of mating with a bishop and knight and some of it just happened to be in line with perfect play. That's all there's to it.

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