INDIAN WELLS, Calif. (AP) — Novak Djokovic and Ana Ivanovic, both 20-year-old Serbs who have joined the ranks of tennis' elite, won matches in straight sets Thursday to move into the Pacific Life Open semifinals.

Australian Open champion Djokovic defeated Stanislas Wawrinka 7-6(5), 6-2 to advance in the men's tournament, and No. 2 Ivanovic beat Vera Zvonareva 6-1, 6-4 on the women's side.

Two-time champion Lindsay Davenport had to retire from her match against Jelena Jankovic after the first set because of a back problem. Jankovic, also from Serbia, won the set 6-2.

Davenport, who has had back trouble in the past, said she thought lingering tightness might go away while she was playing.

"It was pretty obvious to me after two games that I was pretty sore, and it was hard to rotate," she said. "I tried to do the best I could. But sometimes these things happen, and when you're familiar with an injury, you kind of know right away what you're up against."