An Obvious Positional Advantage

Continuing with Petrosian's Exchange Sacrifice, Petrosian evaluated the position shown in the diagram with 'White has an obvious positional advantage'.

Black has a backward Pawn e7, White the strong Knight on c6. The usual method for White is pressure by Rooks along the e-file to force ...e6. After the exchange on e6 Black has new troubles. Without hurry, through positional transformations, White increases his positional plus. The natural order of moves would be Re1 followed by Bf4 or Bg5, depending on Black's reaction, so as to exercise a lasting pressure which could grow step by step.

Instead, Portisch played 24.Bg5.

Now Black could have played 24...Bf6, 24...Nf6, or even 24...Nb8, protecting the attacked Pawn. The move Black cannot dream about is ...f6. But after White's inaccuracy, the idea of ....e5 fascinated me. If White takes en passant, Black can hold the position: he recaptures with the Rook, has the strong Bishop g7, another Rook goes to e8, and the Knights are good.

Petrosian trusted his intuition and played 24...e5.

Portisch thought some ten minutes, looking at me all the time. He couldn't decide whether I had sacrificed an exchange or blundered it away. Finally, after the game, he said he had decided that it was a blunder. Therefore he took the exchange and got a bad position.

How many players wouldn't have taken the exchange?

San Antonio 1972
Petrosian, Tigran

Portisch, Lajos
(After 23...Ne4-c5)
[FEN "4rrk1/1bqnppbp/1pNp2p1/pPnP4/2P5/4BB2/P4PPP/1NRQ1RK1 w - - 0 24"]

The game continued 25.Be7 f5 26.Bxf8 Nxf8.

The position has been changed radically in two moves. White has a Rook for a minor piece but no active play: all the files are closed, while Rooks are valuable only when they operate on open lines. The Black Pawn stands on e5, not e7, so the White Knight is very beautiful, but nothing else. Situations might arise where Black could have an extra piece in action. Unfortunately I failed to win this game, although Black undoubtedly had the edge.

[To be continued]

To play through the complete game see...

Lajos Portisch vs Tigran Vartanovich Petrosian, San Antonio 1972
http://www.chessgames.com/perl/chessgame?gid=1106952

...on Chessgames.com.