Petrosian-Botvinnik, game 5, 1963: More Instructive Moments

Last time I asked you what you would play for White in this chess position:

Of course, you had a hint: The topic of the blog post was 'positional forcing moves'. These are moves that make a positional, rather than tactical threat, and as a result may go unnoticed during a search for candidate moves. However, they are extremely important!

Petrosian played 23.b4!, attacking Black's pawn on c5. Craig Pritchett explains the move very well:

Petrosian takes advantage of White's temporary pin on the c-file, to force either the 'actual' isolation of Black's c-pawn (after an exchange on c5) or its 'artificial' isolation, as in the game. In both cases, Black's c-pawn, while passed, is likely to come under serious long-term attack, should it advance. If it doesn't, White will control the c4 square.

As soon as I saw the move on the board, it made perfect sense. But my friend (who is also a master) and I hadn't predicted it while quickly playing through the game solitaire chess. I think this is a perfect example of a strong positional forcing move.

After 23...c4, 24.b5 showed the idea behind the move: As Craig Pritchett observed, the Black pawn on c4 becomes 'artificially' isolated. It may not officially be an isolated pawn, but it may well be for all intents and purposes: No black pawn will reach c4 to protect it!

Petrosian soon won the pawn - Black could have defended better in time trouble - and the players eventually reached the following position:

What would you do here for White? Solution coming soon!