Top-ranked Victoria Azarenka lost for the first time this year when she was beaten by Marion Bartoli 6-3, 6-3 on Wednesday in the quarterfinals of the Sony Ericsson Open.
Current No. 1 Azarenka was off to the best start on the women's tour at 26-0 since Martina Hingis went 37-0 to begin 1997. An unreliable serve and atypical mistakes from the baseline doomed her against Bartoli.
''I'm a human, not a superwoman, and I wish I could be, but I'm not,'' Azarenka said with a smile. ''I feel disappointed, sure. Who wouldn't be after the loss? But what I've done in the last couple of months, I have to be really proud of myself.''
The steady Bartoli took charge of rallies by playing inside the baseline.
''Sometimes I took the ball extremely early,'' she said. ''It was almost table tennis.''
Seeded No. 7, Bartoli advanced to the Key Biscayne semifinals for the second time in three years. Her opponent in the semifinals Thursday will be No. 5 Agnieszka Radwanska, who eliminated Venus Williams 6-4, 6-1.
The other semifinal will be between Caroline Wozniacki and Maria Sharapova, a three-time Key Biscayne runner-up.
In the men's quarterfinals, No. 2-seeded Rafael Nadal continued his bid for his first Key Biscayne title by beating No. 6 Jo-Wilfried Tsonga 6-2, 5-7, 6-4. His opponent Friday will be 2009 champion Andy Murray, who overcame an upset stomach and early deficit to beat No. 9 Janko Tipsarevic 4-6, 6-3, 6-4.
Venus looked weary Wednesday after winning three consecutive three-set matches. Williams' serve lacked its usual speed, and by the final game she wasn't even chasing after shots in the corner.
The tournament was Williams' first since the US Open last August, where she withdrew after being diagnosed with a fatigue-causing autoimmune disease.
''It was disappointing not to be able to feel my best today,'' Williams said. ''I was able to keep it close in the first set and try different strategies, but it was definitely a mental battle, and today I didn't conquer the mental part of it.''
Eager to keep points short in the 85-degree sunshine, Williams charged the net often but was frequently had to lunge for shots. She committed 38 unforced errors to 10 for Radwanska, and won only five of 26 points on her second serve.
''It was pretty hot out there,'' Radwanska said. ''Maybe that was why she didn't look that good.''
Venus was the second Williams in 18 hours to be eliminated. Younger sister Serena lost Tuesday night to Wozniacki.
Venus is ranked No. 134 and needed a wild card to enter the tournament. The three-time Olympian's goal is to improve her ranking enough to qualify for the London Games, and she's projected to climb next week back into the top 90.
In the past, the cutoff for making the Olympics has been around 68th. It will be based on rankings in early June. Radwanska, ranked a career-best No. 4, advanced to the Key Biscayne semifinals for the first time. She's 0-4 this year against top-ranked Victoria Azarenka and 24-0 against everyone else.
She beat Williams in 2006 but had since lost five consecutive meetings.
''Of course she had some time off last couple of months,'' Radwanska said. ''But she's still a great player. I really had to play very well today to beat her.''
Williams overcame a match point in the third round against Aleksandra Wozniak on Sunday night, and said she was up until 4 a.m. afterward. She recovered to beat No. 15-seeded Ana Ivanovic on Monday.
Williams said her ailment requires her to save all her energy for tennis, but she strayed from that approach with a day off Tuesday.
''I should have rested more probably,'' Williams said. ''After a while you start to feel like maybe everything's behind you. I definitely learned maybe if you're doing something right, don't change it.''
Her energy reserve appeared low from the start of the quarterfinal, and she lost the first seven points. Radwanska took advantage of Williams' lethargy by hitting several drop shots for winners and pouncing on weak second serves.
When Williams had a chance at an easy overhead, she walked up to the ball flat-footed. Facing break point early in the second set, she mustered only a 72-mph first serve, well below her norm of 110 or more.
Williams lost the final six points, dumped her last shot into the net and began looking ahead to the clay-court season. She plans to play next week at Charleston, South Carolina.
''I've definitely learned a lot about ways maybe I could prepare during the tournament,'' she said.
