MASON, Ohio -- Serena Williams woke up with a sore and swollen right big toe on Wednesday, prompting her to withdraw from the Western & Southern Open -- the latest in her long streak of foot problems and setbacks.
Williams had won two straight tournaments at Stanford and Toronto, and her win Tuesday night at the Cincinnati-area tournament was her seventh match in eight days.
She decided to withdraw and rest the foot, which she cut on glass at a restaurant and needed two operations to repair last year. Williams was rounding back into form with the U.S. Open less than two weeks away.
"I don't think this is a good time for me to take a big chance," she said. "I just don't think that would be smart."
Williams is the third high-profile player to miss some or all of the tournament because of injury. Sister Venus Williams withdrew before the start because of a virus that also forced her to sit out the tournament in Toronto. Defending champion Kim Clijsters couldn't play because of an injured abdomen.
The tournament also lost top-ranked Caroline Wozniacki on Wednesday. Wozniacki dropped her opening match for the second consecutive week, falling to American Christina McHale 6-4, 7-5 in the second round.
Williams was trying to win three in a row for the first time since the start of the 2008 season. She's won 12 straight matches, equaling the longest such streak on the WTA Tour this year.
She also seemed to be beyond the foot and other problems that dropped her to No. 175 in the rankings. Her back-to-back tournament titles moved her all the way up to No. 31.
She beat Lucie Hradecka in two sets Tuesday night. She said the toe was sore during the match, but not so much that it was a concern.
When she awoke Wednesday, it was sore and swollen. She talked to her father and her sister before deciding to withdraw and rest for a few days.
"It's not as bad as it was before," she said. "It's just a lot of match play. I've been playing a lot of the matches, more than I have in a long time, and also training as well. It got a little aggravated. Instead of making it worse, I've decided it will be in my best health not to go on."
The time off will also give her the opportunity to attend the wedding of Kim Kardashian, who is marrying NBA player Kris Humphries in California over the weekend. Williams is a friend of the reality TV star.
"Now that I have time, I probably will," she said. "I hadn't thought about it."
After winning her fourth singles title at Wimbledon in 2010, Williams cut her foot on glass at a restaurant, starting a streak of injuries and ailments that kept her away from tennis for nearly a year. Besides the two operations on her foot, she was diagnosed in February with blood clots in her lung. Then, she needed treatment for a pocket of blood that formed under the skin on her stomach.
She wasn't overly concerned about the latest foot problem coming before the U.S. Open.
"What scares me is if I keep going and not listening to my body," she said. "Right now, I'm really in tune and really in touch with that. We have a great relationship."
While Williams was deciding to withdraw, Wozniacki was struggling to keep the ball in play against a qualifier. She also lost her opening match last week in Toronto.
The Dane had never faced the 76th-ranked McHale, who broke Wozniacki in the 11th game of the second set with a delicate drop shot. She clinched the match when Wozniacki sailed a forehand long.
"I can't remember the last time I had two first-round exits," she said. "It's a bit different. You know, I usually play better as the week goes on, but what happens, happens."
Third-seeded Victoria Azarenka withdrew before her evening match because of a strained right hand.
In other results Wednesday, second-seeded Russian Vera Zvonareva defeated countrywoman Ekaterina Makarova 6-3, 6-0; ninth-seeded German Andrea Petkovic beat Sofia Arvidsson of Sweden 6-2, 6-4; No. 13 Jelena Jankovic of Serbia rallied past China's Zheng Jie 4-6, 6-3, 6-1; 14th-seeded Russian Svetlana Kuznetsova defeated Petra Cetkovska of the Czech Republic 4-6, 6-3, 6-4; Nadia Petrova of Russia upset No. 15 Ana Ivanovic of Serbia 6-3, 7-6 (4); No. 16 Peng Shuai of China beat Italy's Sara Errani 6-2, 6-4; and
Petra Martic of Croatia upset No. 17 Yanina Wickmayer of Belgium 3-6, 6-2, 6-2.
Information from The Associated Press was used in this report.