SCOTTSDALE, Ariz. (AP) _ Serena Williams decided to err on the side of caution when her left knee began to act up at the rain-soaked State Farm Women's Tennis Classic on Thursday night.
Williams, the world's top-ranked player and winner of the last four Grand Slam titles, withdrew an hour before her first match because of tendinitis.
``Usually it doesn't hurt this bad,'' Williams said. ``But it was like this during Toronto last year, and I think I made a good decision and pulled out. I went on to do well at the (U.S.) Open, so I just want to make sure my judgment was correct.''
Stephanie Foretz of France, at No. 62 the highest-ranked qualifier to lose in the final round, replaced her. Alexandra Stevenson beat Foretz 6-3, 6-0 and advanced to the quarterfinals.
In other second-round action, Ai Sugiyama stunned third-seeded Lindsay Davenport 7-6 (5), 4-6, 6-3.
Meghann Shaughnessy ousted fourth-seeded Jelena Dokic of Yugoslavia 6-4, 6-2, Laura Granville eliminated fifth-seeded Chanda Rubin and Francesca Schiavone beat fellow Italian Silvia Farina Elia 1-6, 7-5, 6-3.
Second-seeded Kim Clijsters of Belgium was leading Zimbabwe's Cara Black 4-2 in the first set when their match was suspended by rain. Sixth-seeded Eleni Daniilidou of Greece and Joon Jeong Cho of South Korea never got started.
Both matches were rescheduled for Friday.
Williams' withdrawal, coupled with Sugiyama's upset of Davenport, deprived the event of its top two U.S. attractions before the second round ended.
Williams, the defending Scottsdale champion, made an appearance on Stadium Court before leaving for Florida. She gave away two rackets to fans and donated another to a children's hospital for auction, then apologized for pulling out.
Williams beat Jennifer Capriati in three sets to win this tournament last year. It was the first of the 19 singles titles that have made her the WTA's top-ranked player for 34 weeks.
She said the win in the desert worked ``magic'' on her career, which made her reluctant to leave Thursday.
``It was just the beginning of an unbelievable year for me,'' said Williams, who is 11-0 this season, including the Australian Open championship _ her fourth straight Grand Slam title. ``I had a lot of points to defend here, so I'm going to have some points coming off that I would have liked to have staying on.
``I'm not really happy about that.''
All four titles during her ``Serena Slam'' came against sister Venus. The two Florida residents have committed to play in Miami starting March 17, and Serena said she would be ready.
``I have been playing a lot and working hard and doing a lot of off-court stuff,'' Williams said. ``Right now, my body needs a bit of a rest. I'll be able to recharge.''
For the third straight day, rain affected the schedule. The start of play was delayed six hours, and officials tried to squeeze all eight second-round matches into one afternoon and night, but came up short.
The weather may have affected Williams, Davenport and Virginie Razzano of France. Razzano lost the first set of her match 6-4 to eighth-seeded Nathalie Dechy of France, then withdrew because of an upper respiratory infection.
After her loss, Davenport acknowledged she was playing with a cold. ``I felt like I was physically beat,'' she said.
She was 7-0 against Sugiyama, plus a win in a walkover at Oakland in 1995. But Japan's top player rallied from a 4-2 deficit in the first set and came back from 3-1 in the second.
By the final match, Sugiyama was more aggressive, breaking Davenport in the first, seventh and ninth games.
She won the first three points of the ninth before hitting a backhand long, but on match point it was Davenport whose forehand sailed long.
``I don't normally like to play someone who hits the ball very hard and deep, but this time I did,'' Sugiyama said.