White: Lajos Portisch
Black: Anatoly Karpov
1.d4 Nf6 2.c4 e6 3.Nf3 b6 4.a3 Bb7 5.Nc3 d5 6.cxd5 Nxd5 7.Qc2 Nxc3 8.Qxc3 Nd7 9.Bg5
An irritating move to face. 9...f6 is too weakening, 9...Nf6 distracts the knight from its duty of supporting the c5 advance, and 9...Be7 looks highly dubious.
9...Be7! 10.Bxe7 Kxe7!
Essential, since 10...Qxe7 loses a pawn to Qxc7. Such monarchic boldness has not been since since the days of Steinitz.
11.e3 Rc8! 12.Be2 c5!
White must surely have been expecting 11...Re8 and 12...Kf8. Only now does he realise that Black intends to leave his king in the middle of the fray.
13.dxc5 Rxc5 14.Qxg7 Rg8 15.Qxh7 Rxg2
Attempting to punish Black for his presumtuous king advance, white grabbed the offered pawn, but now finds his own king lacking a safe haven. While Black's king elected to stay in the middle, White's is now unpleasantly forced to do so.
16.Qh4+ Nf6 17.Rd1 Qc7 18.Nd4 a5!! (see diagram)
Before playing such a move, Black must stare long and hard at the b4 square as if in fear of a white pawn advancing there. On playing a5, his expression must say: "I know I am weakening b5, but sadly it is necessary." Only then will White's knight come into the parlour.
19.Nb5?? Rxb5! 20.Bxb5 Rg4
With queen and rook now attacked, White must emerge a piece behind.
First confused, then non-verbally disinformed, he stood no chance.