Venus, the defending champion, defeated Jelena Jankovic 5-7, 6-3, 6-4 in one semifinal Saturday at the Sony Ericsson Championships. Caroline Wozniacki retired against Serena in the other because of an apparent abdominal injury while trailing 6-4, 0-1.
Serena, who secured the year-end No. 1 ranking this week, will play for the title Sunday. She is returning to the final of the tournament 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.
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 said Friday her aching abdominal muscles were affecting her serve.
After chasing down a drop shot and hitting a forehand winner for the break, Wozniacki pulled up and told the chair umpire she couldn't continue. The U.S. Open finalist exchanged hugs and handshakes with Serena, explaining her decision with an apologetic smile.
"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."
The Williams sisters are also playing in the four-team doubles event at the season-ending tournament, and took on Spanish duo Nuria Llagostera Vives and Maria Jose Martinez Sanchez in the semifinals later Saturday.
Venus trailed 2-0 in the decisive set against Jankovic but broke the former top-ranked Serb three times in a row en route to a 5-3 lead. The defending champion then saved a break point in the last game before sealing the win with a forehand on a net cord.
"In the first set, I couldn't feel the ball," Venus said. "Just to come back ... to play so well against such a consistent player is great."
Jankovic had just two winners in the first set, but Williams was done in by her inconsistent forehand and 23 unforced errors. She cleaned up her game in the second, hitting a forehand winner to break for 4-2 and holding the next game at love before serving out the set with a 119 mph ace.
Both players finished with more unforced errors than winners - 49 to 43 for Williams and 34 to 17 for Jankovic. Williams' serve was equally inconsistent, mixing 10 aces with 11 double-faults.
It was the ninth three-setter in 10 meetings between the two, with the head-to-head series now 5-5. Their last meeting was also in the semifinals in Doha last year.
Venus Williams reached this year's semis despite winning just one of her three round-robin matches, the first player to do so since Amelie Mauresmo in 2003. She clinched a berth when Svetlana Kuznetsova beat Elena Dementieva in the last group round Friday and now seems determined to make the most of her lucky break.
"This is my last tournament of the year, so I'm giving a thousand percent," she said.
Copyright 2009 The Associated Press.
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