Result: Petra Kvitova through to Istanbul semi-finals

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.