Top seed Victoria Azarenka, who was feeling sick when she played her third round match in Tokyo against Roberta Vinci, had to call it quits today. Azarenka, who has been experience some dizziness, gave Angelique Kerber a walkover in the quarterfinals. Kerber's semifinal opponent will be defending champion and 3rd seed Agnieszka Radwanska. Radwanska beat her friend, Caroline Wozniacki, in straight sets in the quarterfinals.
Meanwhile, 2nd seed Maria Sharapova lost to 10th seed Sam Stosur, who defeated her 6-4, 7-6. Stosur won the tiebreak 10-8. The Australian will face Nadia Petrova in the semifinals; Petrova defeated Sara Errani 3-6, 7-5, 6-3.
Last year, Radwanska won the Tokyo and Beijing titles back-to-back, a feat that is rarely accomplished. Radwanska's fortunes have been mixed lately: She went out in the first round of the Olympic Games, but reached the final of Wimbledon. The Polish star suffered a recurrence of a shoulder injury during the U.S. Open Series, then lost to Vinci in the round of 16 at the U.S. Open. So far, though, she appears to be making the same kind of comeback in Asia that she made last year. In 2011, Radwanska went out in the second round of the U.S. Open.