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.

Passed pawns are also important at the endgame, and even more those who are far away from the king and the rest of pawns. With this sacrifice, Sargissian creates a passed pawn that will leave the knight pretty tied to the rim.

1...Bd8! This was the move that put up more resistance!
1...axb4 2.a5 Kg7 3.a6 Kf8 4.a7 Nb6 5.Ba6 Followed by Bb7 at some point, winning a whole piece.