1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.e4 d6 5.Be2 0-0 6.Bg5 Na6 7.f4 c6 8.Qd2 d5 9.Bxf6 exf6 10.exd5 cxd5 11.Nxd5 Re8 12.Nf3 Be6 13.Ne3 Qe7 14.0-0 Bd7 15.Kf2 Bc6 16.Rae1 Rad8 17.d5 Nc5 18.Bd3 Qc7 19.g3 a5 20.Kg2 Bd7 21.Nd1 f5 22.b3 b5 23.cxb5 Ne4 24.Bxe4 fxe4 25.Nd4 Qc5 26.Nc6 Bxc6 27.bxc6 Rxd5 28.Qf2 Qxc6 29.Ne3 Bd4 30.Qc2 Qxc2+ 31.Nxc2 Bc5 32.Re2 Red8 33.Rc1 f5 34.Kf1 Kf7 35.Ne3 Bxe3 36.Rxe3 Rd1+ 37.Rxd1 Rxd1+ 38.Re1 Rxe1+ 39.Kxe1 When I first replayed the game I was very surprised to see Potkin head for the pawn ending - I assumed that it was lost, and when Grischuk won pretty straightforwardly it seemed even stranger. The only thing I was unsure about was if White could hold by refraining from b3-b4, and once I worked out that there was no salvation there either, it seemed like that was that. Surprisingly, though, a couple of readers noted that the correct evaluation changed twice later on in this ending, so things are clearly not as simple as they seemed at first glance. Let's therefore take a closer look.
39...Ke6 40.Kd2 Kd5 41.Kc3 Kc5 42.a3 Kd5 First decision point: b4, or not b4? (Almost Hamlet, but not quite.)
43.b4 [43.h3 almost draws, but not quite. 43...Kc5! 44.g4 (44.b4+ axb4+ 45.axb4+ Kd5 46.g4 h5 47.gxh5 gxh5 48.h4 Kc6 49.Kc4 Kb6 50.Kc3 (50.b5 e3 51.Kd3 Kxb5 52.Kxe3 Kc4-+ ) 50...Kb5 51.Kb3 e3 52.Kc3 e2 53.Kd2 Kxb4 54.Kxe2 Kc4-+ ) 44...h5!! (It's very subtle, but 44...h6? is a mistake, after which White can survive or at least reach a queen ending with practical drawing chances. 45.g5 h5 46.h4 Kd5 47.Kc2 Kd4 48.Kd2 e3+ 49.Ke2 Kc3 (49...Ke4 50.b4 axb4 51.axb4 Kxf4 52.b5 Ke5 53.Kxe3 Kd5 54.Kf4= Kc5 55.Ke5 Kxb5 56.Kf6 f4 57.Kxg6 f3 58.Kh7 f2 59.g6 f1Q 60.g7 Qf7 61.Kh8 and it's a draw, as Black's queen doesn't have access to h5. Without ...Qh5+, White's king can't be forced in front of the pawn, so it's just a draw.) 50.Kxe3 Kxb3 51.Kd4 a4 52.Ke5 Kxa3 53.Kf6 Kb4 54.Kxg6 a3 55.Kh7 a2 56.g6 a1Q 57.g7 Qa7 58.Kh8 Qd4 59.Kh7 Qxf4 60.g8Q Qg4 Winning? Maybe.) 45.g5 (45.gxf5 gxf5 46.h4 keeps h5 blockaded (see the main lines of the 44...h6 and 44...h5 variations), but it doesn't matter here. 46...Kd5 47.Kc2 (47.b4 axb4+ 48.axb4 Kc6 49.Kc4 Kb6 50.Kd4 Kb5 51.Kc3 e3 52.Kd3 Kxb4 53.Kxe3 Kc4-+ ) 47...Kd4 48.Kd2 e3+ 49.Ke2 Kc3 50.Kxe3 Kxb3 51.Kd4 Kxa3 52.Ke5 Kb4 53.Kxf5 a4 54.Kg6 a3 55.f5 a2 56.f6 a1Q 57.f7 Qh8-+ ) 45...h4! The key move! (45...Kd5? 46.h4 Kc5 47.Kc2 Kd4 - see 44...h6, the position after 47...Kd4.) 46.Kc2 Kd4 47.Kd2 e3+ 48.Ke2 Ke4 49.b4 axb4 50.axb4 Kxf4 51.b5 Ke5 52.Kxe3 Kd5 53.Kf4 Kc5 54.Ke5 Kxb5 55.Kf6 f4 56.Kxg6 f3 57.Kh7 f2 58.g6 f1Q 59.g7 Compare this with the 44...h6 line. Black wins here, but not there, because the h5 square is open. 59...Qf5+ 60.Kh8 Qh5+ 61.Kg8 Kc6 62.Kf8 Qh6 63.Kf7 Qh7 64.Kf8 Kd7 65.g8Q Qe7# ]
43...axb4+ 44.axb4 h6 45.h3 h5 46.h4 All the tempo moves have been used, so the question is whether, when Black plays ...e3 to win the b-pawn and penetrate with his king, he'll be able to obtain the opposition and outflank White's king on the way to winning the g-pawn. To put it concretely, consider a position without White's b-pawn and Black's e-pawn, with White's king on e3 and Black's on c3. If it's Black to move, it's a draw; if it's White's turn, he loses. The question, then, is whether he can finesse things so that it's White move when that position inevitably occurs.
46...Kc6 47.Kc4 Kb6? [47...Kc7! (47...Kb7! is equivalent) 48.Kb3 (48.Kd4 Kb6 49.Kc3 (49.Kc4 Kc6-+ - see 49...Kc6 in the 48.Kb3 line.) 49...Kb5 50.Kb3 e3-+ see the position after 51...e3 in the 48.Kb3 line.) 48...Kb6 49.Kc4 Kc6 50.Kc3 Kb5 51.Kb3 e3 52.Kc3 Ka4 53.b5 Kxb5 54.Kd3 Kb4 55.Kxe3 Kc3 and there it is, Black wins. (If you're not sure how Black wins from here, don't worry - you'll see this position after 51...Kc3 in the game.)]
48.Kb3? [48.b5! draws, as Black has no way to finagle the opposition in the crucial Kc3 vs. Ke3 situation. 48...e3 (48...Kc7 49.Kd4 Kb7 50.Kc3! and holds. c4 and b6 are corresponding squares: Each player will only move his king to "his" square if the opponent's king has gone there first. 50...Kc8 51.Kd4 Kd7 52.Kc3 Ke6 53.Kc4 Violating the rule? No, because Black can't play ...Kb6 here. 53...Kd6 54.Kd4 Kc7 55.Kc3! (Again, not 55.Kc4? , which loses: 55...Kb6 56.Kb4 e3 57.Kc3 Kxb5 58.Kd3 Kb4 59.Ke2!? Kb3! (59...Kc3?? 60.Kxe3= ) 60.Kxe3 (60.Kd3!? e2 61.Kxe2 Kc2-+ ) 60...Kc3-+ ) 55...Kb6 56.Kc4! Now it's time, and while Black can go round and round some more he'll eventually have to play 56...e3 , which leads to a draw because White gains the opposition at the crucial moment. 57.Kd3 Kxb5 58.Kxe3 Kc4 59.Ke2= ) 49.Kd3 Kxb5 50.Kxe3 Kc4 51.Ke2 Kc3 (51...Kd4 52.Kd2= ) 52.Ke3= This time it's White who has the opposition, and thereby draws.]
48...Kb5 Now it's routine.
49.Kc3 e3 50.Kd3 Kxb4 51.Kxe3 Kc3 Black has the opposition...
52.Ke2 Kc2 and has it once again, which he will use to outflank White's king and draw nearer to the tasty morsel on g3.
53.Ke3 [53.Ke1 Kd3 54.Kf2 Kd2 transposes to the game.]
53...Kd1 54.Kf2 Kd2 Opposition again.
55.Kf3 [55.Kf1 Ke3 56.Kg2 Ke2 And again. 57.Kg1 Kf3 58.Kh2 Kf2 One last time. Finally, Black wins with zugzwang after 59.Kh3 Kg1-+ ]
55...Ke1 56.Ke3 [56.Kg2 Ke2 wins - see the note to White's 55th move.]
56...Kf1 57.Kf3 [Going for counterplay is way too slow. 57.Kd4 Kg2 58.Ke5 Kxg3 59.Kf6 Kxf4 60.Kxg6 Kg4-+ ]
57...Kg1 The White king is squeezed out, and Black's rapacious monarch will devour all the commoners. 0-1