11...dxc4! is the best option. 12.Bxc4 Qc7 White is naturally a bit better because of the bishop pair, but at least the structure is symmetrical, and Black is very solid.
White centralizes the queen, blocking the isolated pawn, using the fact that there is no black piece that can attack it.
The best move. Usually, when one is playing against an isolated pawn, it is a good idea to block it. In this case, the plan would be to block with a knight on d4. After ...Qxc5, Black increases control over the d4-square.
After 19...Nxc5 Black abandons the d4-square, and White would be slightly better.
There was nothing wrong capturing with the rook, but this is even stronger. With the knight coming to c4 White has to be slightly more careful.
Unity Chess Club
Anatoly Karpov Zoltan Ribli Amsterdam 1980 White to move
Black is suffering some pressure on the queenside and Karpov finds a plan to immobilize his opponent!
The best move! Black was intending to play a6! For instance after 19.Kf1?! Black can play 19...a6! 20.Rxb6 20.Rb3 b5 and Black has managed to equalize. Rxb6 Bxb6.
This is the key. The pawn on b2 was hanging after the trade of rooks!
Black has played very passively, and now Karpov simply improves his position choking his opponent.