Serena Williams survived an injury scare in Istanbul yesterday to make a winning start in her bid to cap a brilliant comeback season by regaining the WTA Championship title in the tour’s season-end event.

The Wimbledon, US Open and Olympic champion ap-peared to pull a muscle in the first set but played through the discomfort to overcome Ange-lique Kerber, a debutant in this top eight event.

Williams’s tenacious efforts eventually earned her a 6-4, 6-1 revenge over the improving German left-hander, who up-set the American tennis legend in their last meeting, at Cincinnati two months ago.

Kerber was surprisingly aggressive while coming back from 0-3 to 3-3 in the first set, and also played some fine rallies while earning three chances to reach 5-5.

But she could not convert any of them, and once Williams broke for 3-1 in the second set, the match quickly slid away from the woman from Kiel.

Earlier, the chances of the title changing hands increased significantly when Petra Kvitova, the defending champion, produced a downbeat performance to lose 6-3, 6-2 to Ag-nieszka Radwanska.

Other result: Sharapova bt Errani 6-3, 6-2.