Fortress • Keres - Portisch, Moscow 1967

A potential fortress position was pointed out by Garry Kasparov in 'My Great Predecessors, Part 3', in the chapter on Petrosian (p.124). The position was analyzed in the subsection on Portisch, which is why the ninth World Champion doesn't figure as one of the players.

The position is bad for White. Both the b- and e-Pawns are weak and subject to capture.

Moscow 1967
Portisch, Lajos

Keres, Paul
(After 44...Bf8-h6)
[FEN "8/8/3k2pb/1pn1p2p/pNp1P3/P1P1NK1P/1P4P1/8 w - - 0 45"]

Kasparov didn't say at which point the game had been adjourned, but Keres found the next move during his adjournment analysis. It is entirely possible that Portisch also looked at the sequence during adjournment. 45.h4! Nd3 46.Nd1. Here Kasparov noted that 46.Nxd3? loses after 46...cxd3 and 47...Kc5. 46...Bc1 47.Ke2!. The punctuation is all Kasparov's.

Kasparov: 'It transpires that after 47...Nxb2? 48.Nxb2 Bxb2 49.Kd2 Bxa3 50.Kc2 White has a fortress: 50...Bxb4 51.cxb4 and the remaining White Pawns create an impenetrable barrier in front of the Black King, or 50...g5 51.g3! Kc5 52.Na6+ Kb6 53.Nb4 with a draw.'

Portisch avoided the fortress with 47...Nc5. After 48.Kf3 g5!, he eventually won on the 90th move. To play through the complete game see...

Paul Keres vs Lajos Portisch, Moscow 1967
http://www.chessgames.com/perl/chessgame?gid=1073169

...on Chessgames.com.