39.Kf1 Kb4 40.Ke1 b5 41.f3 Ka3–+.

If White succeeds in lifting the blockade on d6, his passed pawn will become very strong. He can do this with his knight, for example via d2 to c4. Therefore, Black starts play on the dark squares:

With this move, Black gets rid of an ‘unnecessary’ piece, and not only strengthens his blockading knight, but the whole complex of dark squares. It is important that now the white Bf3 becomes a bad piece, blocked in by its own d5-pawn.

A serious positional mistake, after which White is left with a bad bishop against a beautiful knight. It was essential to decline the exchange, and retreat the bishop to d2 or e3 – in this case, White would retain counterplay, since then Black does not get a free hand for major-piece play on the dark squares.

After an exchange of dark-squared bishops, outposts appear on e5, e3 and g5 – Black happily exploits them.

Now, the blockade is lifted, and Black’s advantage disappears with it.

Objectively, White’s position is somewhat better. As is well-known, the queen is a poor blockader. In addition, the white pieces are already on strong squares. The direct idea of transferring the knight from f6 to d6 either fails tactically, or is met by a basic refutation in the form of the move Bc2-a4 and the exchange of the knight on e8, with an obvious advantage to White.

Black goes for the sacrifice, to exchange some major pieces.

An important move. Black gives up a pawn, but exchanges all the rooks.