U.S. Open champion Samantha Stosur defeated Lucie Safarova of the Czech Republic 6-1, 6-7 (5), 6-1 Wednesday to advance to the third round of the Dubai Tennis Championships.

Defending champion Caroline Wozniacki topped Romania's Simona Halep 6-2, 6-3. She'll face Ana Ivanovic, who defeated Maria Kirilenko of Russia, 6-2, 7-6 (4).

Stosur broke twice in the first and third sets and saved all nine break points she faced in the match. She will meet Jelena Jankovic of Serbia in the third round on Thursday. Jankovic defeated Italy's Flavia Pennetta 7-5, 6-4.

Jankovic beat Stosur in the quarterfinals in the Dubai tournament last year.

"Good chance for me to try and bounce back from that loss," Stosur said. "I think I've got to really step up and play aggressive and realize she's not going to make too many errors."

Earlier Wednesday, top-ranked Victoria Azarenka pulled out of the Dubai tournament because of a left ankle injury. The Australia Open champion, who has won 17 straight matches this season, says she will rest for two or three days.

"Obviously, it's very disappointing. But, I mean, it's life. It's sport," Azarenka said. "I just have to take care of it. Hopefully, it will settle down."

Azarenka said she injured her left ankle during last week's semifinal match at the Qatar Open. Azarenka shook off the injury to beat Stosur in the final.

Sabine Lisicki of Germany also advanced after defeating Iveta Benesova of the Czech Republic 6-3, 6-3. Lisicki will play Agnieszka Radwanska, who defeated Israel's Shahar Peer 7-5, 6-4.

Azarenka said the packed tennis schedule and increasingly tough competition could be the cause of injuries among the players.

Wimbledon champion Petra Kvitova, French Open winner Li Na and Vera Zvonareva also pulled out the Dubai tournament because of injury or illness.

"For me, obviously I played so much, and it was an unfortunate situation what happened in Doha," Azarenka said. "But I mean, it's just the game became so physical. Sometimes it's really tough on the body week after week to play.

"For example, these tournaments back-to-back with such a tough field, it takes a lot out of you physically."

Wozniacki was No. 1 until Azarenka unseated her last month by winning the Australian Open. She said she hopes her Belarusian friend recovers from the injury after a good rest.

"Vika has had a great start to the year. I'm sure her body is feeling very tired at the moment, and she needed the rest before Indian Wells," Wozniacki said. "You know, injuries happen in tennis. Just need to be happy when you're healthy."