Annotated chess game

Isn't this the Tarrasch line?

A point to note here is that Black has accepted the slight disadvantage of an isolated d-pawn (a.k.a. "IQP" or "isolani") in the hope and expectation that the plenty of room available for active piece play will more than balance this weakness. For the moment, Petrosian plays to restrain the d-pawn preparatory to building up an attack against it.

The suggested alternative offers to exchange off Black's "good" bishop, reducing his mobility somewhat. On the other hand, it does leave the d-pawn less amenable to restraint. Instead, White elects to blockade the d-pawn, with the propect of exchanging on c6 to leave Black with a hanging pawn couple sitting on files half-opened for White's rooks.

The purpose of 18.a5! was to prevent the b3-knight at once attacking the c-pawn by Na5. Instead of 20.Nd2? White might have done better to have blockaded the rearward pawn of the pawn couple by 20.Nc5 - a powerful post for the knight, which, among other things, would have kept the pawn couple immobile for the time being.

During this 10-move sequence, Black is straining every nerve to mobilise his pawn-couple, White to hold it back. Though Black's game is the freer, the inherent weakness of Black's hanging pawns keeps White in the game.

Not so easy to spot: 33.e4? Qe2 34.exd5 c4 35.bxc4 Bb4 wins the d2-bishop. White would find it a very uphill battle to save the draw from here!

Black might have tried, instead of 38...Bd6, 38....h4, hoping that White would weaken the dark squares by 39.g5. But the straightforward 39.gxh4 reduces Black's influence on the dark squares, given that White retains his own DSB.

I'm not sure what is meant by "winning on position". Black has the more space, but that doesn't mean much with so little material remaining on the board. Maybe Black has something of the initiative as well, but the chances of achieving anything positive look pretty slender.