Petra Kvitova has made it through to the semi-finals of the WTA Championships in Istanbul after a straight-sets win over Agnieszka Radwanska.
The Czech will now face Sam Stosur in the final four after her win against Li Na.
Radwanska needed to secure a set to progress to the next stage of the round robin tournament but was edged out of the first set 7-6 in the tie-break.
The second was more straightforward for Wimbledon champion Kvitova, who took it 6-3.
