Was this Kramnik's mistake? [fen ""]
[title "A. Grischuk vs. V. Kramnik, FIDE Candidates 2018 (Mar 19, 2018)"]
[startply "140"]

1. c4 e6 2. Nc3 d5 3. d4 Nf6 4. Nf3 c5 5. e3 dxc4 6. Bxc4 a6 7. Bb3 b5 8. e4 cxd4 9. Nxd4 Bb7 10. e5 Ne4 11. O-O Nxc3 12. bxc3 Nc6 13. a4 Bc5 14. axb5 axb5 15. Rxa8 Bxa8 16. Nxb5 O-O 17. Qxd8 Rxd8 18. Bf4 h6 19. h4 Ne7 20. Rd1 Rb8 21. Bc4 Bc6 22. Nd4 Be4 23. h5 Nd5 24. Bxd5 Bxd5 25. Be3 Rc8 26. Re1 Bc4 27. Nf3 Ba3 28. Bd4 Bd3 29. Nd2 Bb2 30. Nf1 Rc4 31. Re3 Bf5 32. Ng3 Bh7 33. Kh2 Bc1 34. Re2 Bf4 35. Kh3 Ra4 36. Kg4 Bc1 37. Kf3 Bd3 38. Re1 Bb2 39. Ke3 Bc2 40. Kd2 Bb3 41. Rb1 Ra2 42. Kd3 Ba4 43. Ne4 Ba3 44. Ke3 Bc2 45. Re1 Bb3 46. g4 Bd5 47. Kd3 Be7 48. Rb1 Ra8 49. f4 Bh4 50. Rh1 Bd8 51. Rb1 Bc7 52. Ke3 Kh7 53. Nd6 Kg8 54. Rb5 Bc6 55. Rb4 Bd8 56. Bb6 Bh4 57. Bd4 Bg2 58. Rb2 Bc6 59. Rb6 Bg2 60. Rb2 Bc6 61. Rb3 Bg3 62. c4 Bh2 63. f5 exf5 64. Nxf5 Kh7 65. Bb2 Re8 66. Nd6 Re7 67. Rb8 f6 68. Rc8 Bh1 69. Nf5 Rb7 70. exf6 Rb3+ 71. Bc3 gxf6 72. Kd2 Bf4+ 73. Kc2 Rb8 74. Rxb8 Bxb8 75. Ne7 Be4+ 76. Kd2 Bf4+ 77. Ke2 Kg7 78. Nf5+ Kf7 79. Bd2 Be5 80. Bxh6 Ke6 81. Be3 Bxf5 82. gxf5+ Kxf5 83. h6 Kg6 84. c5 f5 85. Kf3 Kf7 86. Bf4 Bd4 87. c6 Ke7 88. c7 Kd7 89. h7 Kc8 90. Ke2 Kd7 91. Kd3 1-0


I'm looking at yesterday's game between Grischuk and Kramnik, and I'm trying to understand (disclaimer: I'm a weak recreational player) where did Grischuk make the difference. Is it right to say that Kramnik blundered on move 70? Or was the game lost earlier? 

(Game from Chess.com)
I entered the position in ChessBase and got Komodo 9 to analyze it -- it says 70...Rb3+ was Black's best move by far, only giving White a +0.64 advantage (which means the engine thinks White is "64% of a pawn" better). The reason Rb3+ is a good move is that Black needs counterplay -- if he sits and does nothing, White will win easily (due to being up 2 pawns).

So, at that point the game was close to drawn, but White still had good chances to press and win (which he did).

Black's mistake was playing 76...Bf4+, giving White a winning advantage. Instead, he should have played 76...Bf3, attacking White's g4-pawn. Playing 76...Bf4+ allowed White to play 77. Ke2, stopping Black from playing Bf3.

It's important to note though that Kramnik's mistake isn't close to a blunder -- rather's it's a small inaccuracy that lost the game (at GM level this can happen). It's easy to analyze a game with an engine and criticize the play of even the top players in the world.

EDIT - I checked again on the engine, and Black should play 75...Bf3 instead of 75...Be4+ 76. Kd2 Bf3, since that just brings White's King one square closer.