This is the key. The pawn on b2 was hanging after the trade of rooks!

The idea is rather simple, to play Rba4 and Bxb6!, winning a pawn.

Black has played very passively, and now Karpov simply improves his position choking his opponent.

This is how the game finished. Clinical technique from Karpov.

The best move. White opens the a-file for the rook and the knight on c3 is threatening to jump to e4, which forces Black to play ...d5

10.Nxb5?! Bxb5 11.axb7 Ne7= Black gets rid of the bad bishop on d7.

Developing a piece and putting pressure against c5.

White doubles heavy pieces on the a-file to put tremendous pressure against a7.