Williams has not lost to Sharapova since 2005 and is 5-2 overall against her. This was their first meeting on clay — Sharapova was coming off her first victory on clay last week at Amelia Island. "It was an up-and-down match," said Williams, trying for her third tour title this year. "I don't think I played my best. Actually, I played far from my best." She said she wasn't bothered by an ankle she sprained during a match Thursday. No. 9 seed Vera Zvonareva also advanced to the semis, upsetting defending champion Jelena Jankovic 6-2, 3-6, 6-2.
Zvonareva lost to Jankovic in the semifinals earlier this year in Miami. The two have split their six career matches.
"She's one of the world's top players," Zvonareva said. "I just tried everything that I didn't try in Miami, I guess, and it worked better for me today."
Zvonareva, ranked No. 17, meets fourth-seeded Elena Dementieva and Williams faces unseeded Alize Cornet of France in the $1.3 million tournament on Saturday. Dementieva beat No. 7 seed Patty Schnyder 6-4, 6-4 and Cornet eliminated Agnes Szavay of Hungary 7-5, 6-4.
Williams' best finish at this event was runner-up five years ago, the same year Sharapova made the field as a 15-year-old qualifier and lost in the first round.
Williams struggled in the first set, which featured several long games. She won one game after it went to deuce seven times. But in the third set, Sharapova won just four points in the first five games.
"I gave it all I had in the first two and I think I ran a little bit short," the world's fourth-ranked player said. "My body is adjusting to the clay faster. I'm moving on it a lot better than I used to."
Cornet, an 18-year-old in her second season on the tour, also reached the semifinals at Amelia Island last week. Ranked No. 40, she has never faced Williams but watched her play Friday.
"I said 'Oh my God, if I play Serena tomorrow, I hope not to be ridiculous,'" she said. "I think I will do what I do usually. I will use my topspin forehand. I will run everywhere I can and I will just do my best and fight on every point."