BALI - Ana Ivanovic suffered an injury scare as she began the defence of her title at the Tournament of Champions with a 6-3 6-3 win over Italy's Roberta Vinci.

The Serbian took the opening set with ease, surrendering just seven points in the first four games, but then fell on the baseline three points into the second set.

She received treatment to her right ankle after the third game but brushed off the setback to dominate the remainder of the match, allowing Vinci only four points in the last three games.

"It was a bit sore, but actually when I was moving it was feeling better" Ivanovic told reporters. "So I tried to keep my breaks quite short and walked up the other end to keep it moving.

"It's sore when I put weight on it but I've been to the physio and hopefully it will be fine. We're trying the best with ice and compression and to keep my foot elevated."

Ivanovic, who will celebrate her 24th birthday in Bali on Sunday, will play Nadia Petrova in the semi-finals after the Russian upset Chinese second Peng Shuai 6-4 6-3.