DOHA, Qatar — The Williams sisters will end their season with another title matchup.

Venus Williams defeated Jelena Jankovic, 5-7, 6-3, 6-4, yesterday in one semifinal at the Sony Ericsson Championships. Serena Williams won the other when Caroline Wozniacki quit because of an abdominal injury while trailing, 6-4, 0-1.

Serena, who secured the year-end No. 1 ranking this week, is returning to the final of the WTA Tour's season-ending championships for the first time since 2004. She was knocked out in the group stage the last two years, but was the only player to go undefeated through the round-robin rounds this time.

"I just came in here trying to do my best, and here I am," she said.

Serena won the event in 2001 and has been runner-up twice. Venus will defend her title from last year.

"It's wonderful, I'm so excited," Venus said. "It's the way I wanted to end my year."

Serena beat Venus in this year's Wimbledon final, the fourth time they played each other for that Grand Slam title.

The American sisters were back on the court about 30 minutes after Serena's win yesterday to compete in the four-team doubles event. They missed out on a second final, however, losing to Spaniards Nuria Llagostera Vives and Maria Jose Martinez Sanchez, 2-6, 6-4, 10-8, after a champions tiebreaker.

Wozniacki received medical treatment on her stomach in the first set and quit after breaking Williams to start the second. The 19-year-old Dane has been battling injuries all week, and reiterated after the match that aching abdominal muscles were affecting her serve.

"She's been struggling throughout the entire tournament," Serena said. "She's just an incredible fighter to come out here today and put up an effort."

ELSEWHERE

BA Tennis Trophy: Top-seeded Marin Cilic of Croatia and Jurgen Melzer of Austria won semifinal matches yesterday and will play for the BA Tennis Trophy title in Vienna. Cilic beat Philipp Kohlschreiber of Germany, 6-4, 7-6 (4), while Melzer, seeded seventh, rallied past Janko Tipsarevic of Serbia, 4-6, 7-6 (5), 6-4.

Lyon Grand Prix: Third-seeded Ivan Ljubicic defeated Arnaud Clement, 6-2, 6-4, yesterday to reach the final of the Lyon Grand Prix in Lyon, France, where he'll play wild card Michael Llodra. Llodra beat fellow Frenchman and second-seeded Gilles Simon, 6-7 (4), 6-3, 7-6 (1).

St. Petersburg Open: Two-time Grand Slam champion Marat Safin lost to qualifier Andriy Stakhovsky, 6-4, 4-6, 6-4, yesterday in the St. Petersburg Open semifinals in St. Petersburg, Russia. The 93rd-ranked Stakhovsky will play eighth-seeded Horacio Zeballos, who beat Igor Kunitsyn, 7-6 (7), 6-3.