Fortress? • Korchnoi - Spassky, Belgrade 1977

I like fortress positions. They make nonsense of the relative value of the pieces (P=1, B/N=3 etc.) and they are almost impossible for computers to foresee. Here's one that I had seen before, but forgot until I reviewed the games of the 1977 Korchnoi - Spassky match.

Black's position looks desperate and indeed it is, or was. White's last move let Black escape with a draw, although only a very good player would see the resource involved.

Belgrade 1977
Candidates Final, Game 1
Spassky, Boris

Korchnoi, Viktor
(After 41.Nb4-c6)
[FEN "7r/2Pbkpp1/1N2p3/2R4p/8/6P1/5PKP/8 b - - 0 41"]

Black played 41...Kd6!. Now White wins a piece with 42.c8=Q Bxc8 43.Rxc8 Rxc8 44.Nxc8+. Here's the surprise. After 44...Kc7, the Knight can't escape. Since the sequence 45.Na7 Kb6 46. Nc8+ Kc7 leads nowhere, White tried 45.Ne7. Black chased the Knight down the Black Kingside with 45...Kd7. After 46.Ng8 h4 47.g4 Ke8 48.Kh3 Kf8 49.Nh6 gxh6 50.Kxh4 Kg7 51.Kg3 Kg6 52.Kf4 f6 53.h3 the game was agreed drawn.

While this isn't a typical fortress, I think it qualifies. Instead of an impenetrable position keeping the opponent's pieces out, Black has an airtight position keeping White's piece bottled up. What do you think? To play through the complete game see...

Viktor Korchnoi vs Boris Spassky, Belgrade 1977
http://www.chessgames.com/perl/chessgame?gid=1082376

...on Chessgames.com.