TOKYO — Sam Stosur beat Maria Sharapova 6-4, 7-6 (10) Thursday at the Pan Pacific Open, knocking the two-time champion out to reach the semifinals.
Top-ranked Victoria Azarenka withdrew after a bout of dizziness in her third-round match on Wednesday, advancing Angelique Kerber of Germany to the semis.
Nadia Petrova of Russia, down 6-3, 4-1, overcame sixth-seeded Sara Errani of Italy 3-6, 7-5, 6-3, and will play Stosur on Friday.
Former No. 1 Caroline Wozniacki faced third-seeded Agnieszka Radwanska of Poland in the late quarterfinal.
Stosur broke Sharapova to go up 5-3 in the second set but then lost nine straight points as Sharapova sent the match to a tiebreaker, which Stosur won on her fifth match point when Sharapova returned long.
"I knew that I had lost nine points and was just trying to stop the momentum swing," Stosur said. "I wasn't thinking about the points I lost but was focusing on how I was going to make the next points."
It was only Sharapova's second loss in 11 matches against the Australian, who is in her first semifinals since the French Open.
Sharapova, who won this tournament in 2005 and 2009, struggled with her serve and had five double faults.
"She played a very steady game and I had a few more unforced errors than I would have liked," she said. "It's disappointing to lose but you have to take every disappointment and turn it into a positive. It's really about thinking what I can do to improve for the next tournament."
Azarenka said she hasn't been feeling well for several days.
"Before the tournament on Sunday I was starting to feel not really good," Azarenka said. "I haven't really been doing better since then. Just low energy, you could tell by the matches I wasn't my usual self. But it took too much energy over the last two matches to really push and today it's just not really possible for me."