Game 6 of the 2018 World Chess Championship between Magnus Carlsen and Fabiano Caruana reached a complex endgame.
It is not uncommon for even top players to miss subtle winning ideas in complex endgame positions, especially under the pressure of the World Championship match.
The Position
Caruana had this position with black to move on the 68th move:
FEN: 5k2/8/5pK1/5PbP/2Bn4/8/8/8 b – – 8 68
PGN: 1. e4 e5 2. Nf3 Nf6 3. Nxe5 d6 4. Nd3 Nxe4 5. Qe2 Qe7 6. Nf4 Nc6 7. Nd5 Nd4 8. Nxe7 Nxe2 9. Nd5 Nd4 10. Na3 Ne6 11. f3 N4c5 12. d4 Nd7 13. c3 c6 14. Nf4 Nb6 15. Bd3 d5 16. Nc2 Bd6 17. Nxe6 Bxe6 18. Kf2 h5 19. h4 Nc8 20. Ne3 Ne7 21. g3 c5 22. Bc2 O-O 23. Rd1 Rfd8 24. Ng2 cxd4 25. cxd4 Rac8 26. Bb3 Nc6 27. Bf4 Na5 28. Rdc1 Bb4 29. Bd1 Nc4 30. b3 Na3 31. Rxc8 Rxc8 32. Rc1 Nb5 33. Rxc8+ Bxc8 34. Ne3 Nc3 35. Bc2 Ba3 36. Bb8 a6 37. f4 Bd7 38. f5 Bc6 39. Bd1 Bb2 40. Bxh5 Ne4+ 41. Kg2 Bxd4 42. Bf4 Bc5 43. Bf3 Nd2 44. Bxd5 Bxe3 45. Bxc6 Bxf4 46. Bxb7 Bd6 47. Bxa6 Ne4 48. g4 Ba3 49. Bc4 Kf8 50. g5 Nc3 51. b4 Bxb4 52. Kf3 Na4 53. Bb5 Nc5 54. a4 f6 55. Kg4 Ne4 56. Kh5 Be1 57. Bd3 Nd6 58. a5 Bxa5 59. gxf6 gxf6 60. Kg6 Bd8 61. Kh7 Nf7 62. Bc4 Ne5 63. Bd5 Ba5 64. h5 Bd2 65. Ba2 Nf3 66. Bd5 Nd4 67. Kg6 Bg5 68. Bc4 Nf3 69. Kh7 Ne5 70. Bb3 Ng4 71. Bc4 Ne3 72. Bd3 Ng4 73. Bc4 Nh6 74. Kg6 Ke7 75. Bb3 Kd6 76. Bc2 Ke5 77. Bd3 Kf4 78. Bc2 Ng4 79. Bb3 Ne3 80. h6 Bxh6
Above we have the FEN and PGN of the full game.
While both players thought this was a draw or a fortress, GM Ian Rogers noted that there was a winning idea in the position in the ensuing press conference.
What Needed to Happen for Caruana to Win
Basically, what needs to happen is that:
- black needs to get its king on g8 to remove all legal moves for the white king (this is hard due to the light-squared bishop)
- get its knight on g1 on the edge of the board
- force zugzwang and lose a move (triangulation) to get the h-pawn forward down the board so it can eventually be taken
- if black can take the h-pawn it will win the game.
Stockfish offers this continuation:
1… Bh4 2. Bd5 Ne2 3. Bf3 Ng1 4. Bd5 Bg5 5. h6 Nh3 6. Bb3 Nf4+ 7. Kh7 Ng2 8. Kg6 Nh4+ 9. Kh5 Nxf5 10. h7 Kg7 11. h8=Q+ Kxh8 12. Kg6 Ne7+ 13. Kh5 Kg7 14. Kg4 Nc8 15. Bc2 Kf7 16. Bb1 Bc1 17. Bc2 Nd6 18. Bd3 Ke6 19. Bg6 Nc4 20. Bf5+ Ke5 21. Bg6 Ke6 22. Bf5+ Ke7 23. Bb1 Nd6 24. Bd3 Kf7 25. Bc2 Kg7 26. Bd3 Kh6 27. Bc2 Nc4 28. Bb1 Ne3+ 29. Kf4 Bd2 30. Be4 Kg7 31. Bb1 Nd1+ 32. Kf5 Nc3 33. Bc2 Kf7 34. Bd3 Ke7 35. Bf1 Na4 36. Bd3 Bg5 37. Be2 Bc1 38. Bh5 Nc5 39. Bg4 Ba3 40. Bf3 Ne6 41. Bg4 Ng5 42. Bh5 Bb2 43. Bd1 Nf7 44. Bc2 Nd6+ 45. Kf4 Bc1+ 46. Kf3 Ke6 47. Bh7 Ke5 48. Ke2 f5
This is inefficient but it gets us to a position where white is forced to take the f-pawn or risk worsening its position. The knight would then take the bishop.
Bishop and Knight Checkmate
After this, it boils down to a bishop and knight checkmate.
Once we get to this position, the computer can now spot checkmate-in-25.
Then it’s a matter of executing it.
Black wants the white king in the same corner of the board as the color of its bishop – so get the king to a1 or h8.
Here are the final moves.
One Possible Move Sequence for a Caruana Victory
While the checkmate from move 68 in Game 6 of the 2018 World Chess Championship between Fabiano Caruana and Magnus Carlsen shouldn’t take another 77 moves, in our computer analysis of it, that’s how long it took.
To be precise, here’s the move order:
1… Bh4 2. Bd5 Ne2 3. Bf3 Ng1 4. Bd5 Bg5 5. h6 Nh3 6. Bb3 Nf4+ 7. Kh7 Ng2 8. Kg6 Nh4+ 9. Kh5 Nxf5 10. h7 Kg7 11. h8=Q+ Kxh8 12. Kg6 Ne7+ 13. Kh5 Kg7 14. Kg4 Nc8 15. Bc2 Kf7 16. Bb1 Bc1 17. Bc2 Nd6 18. Bd3 Ke6 19. Bg6 Nc4 20. Bf5+ Ke5 21. Bg6 Ke6 22. Bf5+ Ke7 23. Bb1 Nd6 24. Bd3 Kf7 25. Bc2 Kg7 26. Bd3 Kh6 27. Bc2 Nc4 28. Bb1 Ne3+ 29. Kf4 Bd2 30. Be4 Kg7 31. Bb1 Nd1+ 32. Kf5 Nc3 33. Bc2 Kf7 34. Bd3 Ke7 35. Bf1 Na4 36. Bd3 Bg5 37. Be2 Bc1 38. Bh5 Nc5 39. Bg4 Ba3 40. Bf3 Ne6 41. Bg4 Ng5 42. Bh5 Bb2 43. Bd1 Nf7 44. Bc2 Nd6+ 45. Kf4 Bc1+ 46. Kf3 Ke6 47. Bh7 Ke5 48. Ke2 f5 49. Bxf5 Nxf5 50. Kf2 Kf4 51. Kg2 Ke4 52. Kf2 Kf4 53. Kg2 Ke3 54. Kg1 Kf3 55. Kh2 Bf4+ 56. Kg1 Kg3 57. Kf1 Be3 58. Ke2 Kf4 59. Kd3 Nd6 60. Kc2 Ke4 61. Kc3 Bd4+ 62. Kd2 Nf5 63. Ke1 Ng3 64. Kd2 Ba1 65. Kc2 Kd4 66. Kb3 Bc3 67. Kc2 Kc4 68. Kd1 Kd3 69. Kc1 Nf5 70. Kb1 Kc4 71. Kc2 Ne3+ 72. Kb1 Kb3 73. Kc1 Bb4 74. Kb1 Bd2 75. Ka1 Nc2+ 76. Kb1 Na3+ 77. Ka1 Bc3# 0-1
This would have come to 145 moves in the actual game had it occurred.
Of course, there is more than one way to do things and this is just one way Caruana could have won Game 6 over Carlsen in that match.
