Petra Kvitova has beaten Agnieszka Radwanska in straight sets at the WTA Championships in Istanbul.

The Czech progressed with a 6-4 6-4 win over Radawanska in a match that lasted two hours and 12 minutes on the indoor court.

Kvitova eventually clinched it after a lengthy rally ended with Radwanska over-hitting a return after a back-and-forth final game.

The world number seven will now play Serena Williams in the next round after the American overcame Angelique Kerber in just over an hour in the day's earlier game.