It could have gone this way: 1.f5!! exf5 (1.- gxf5 2.h5 +-) 2.e6 Bxe6 (2.- fxe6 3.Kxg6 +-) 3.h5 gxh5 4.g6 fxg6 5.Kxe6 White has won a piece now for four pawns. According to GM Rogozenco on chessbase.com "both opponents saw this idea, but they both thought it's a draw because a8 is the 'wrong' coloured corner".
The bishop is indeed the wrong one but the black king will not get into the corner, since after 5.- Kd8 6.Kd5 Kc8 6.Kc6 (see diagram 2) he cannot make progress!
The white a-pawn finally queens with check and mate. Black is missing one move because he has to play g5 first before he can play f4. A very funny variation that could have brought Gelfand some glory - if he just had played it.
For the record, the game ended draw after 1.a4.
