Caroline Wozniacki fought through an injury to her right knee Thursday to beat Dominika Cibulkova 6-2, 6-1 in the quarterfinals of the New Haven Open.
The third-seeded Dane improved to 20-0 at the Connecticut Tennis Center where she is the four-time defending champion and looking to become just the fourth woman to win the same WTA event in five consecutive years.
It was unclear Thursday if she would be able to continue her title defense.
Wozniacki said that after hitting a backhand return in the first game of the second set she felt a twinge in her knee that was serious enough to call for the trainer. After a Cibulkova double fault on the next point, Wozniacki walked to the chair umpire, motioned to her knee, sat down and grabbed a bag of ice from a cooler.
''I decided straightaway after I felt it,'' she said. ''I played one more point and decided I needed to see the trainer because I felt a sharp pain in there. I needed to treat it.''
Wozniacki had the knee taped and returned to the court. She seemed to have a slight limp at times, flexed her leg between points and looked over to the coach's box several times seeking guidance.
She planned to get the knee examined later Thursday to determine the extent of the injury before deciding whether to play against Maria Kirilenko in the semifinals Friday.
''You need to judge whether you can continue or you cannot,'' she said. ''You need to judge whether it's going to get worse or it's not. That's all decisions you need to make yourself, decisions that are important because you don't want to jeopardize long-term injury. Doesn't matter what tournament it is.''
Cibulkova said she was distracted by the injury and it affected the rest of the match. She won that first game of the set, but dropped the next six.
''I was paying too much attention to her,'' Cibulkova said. ''When you ask for a physio like this, I was serving, it was my game, it was during the game, it doesn't happen often. When you do it, it has to be serious. You really either cannot move or you cannot continue or something like that.''
Kirilenko, who reached the quarterfinals when German Mona Barthel withdrew with a stomach bug, beat qualifier Olga Govortsova 6-1, 6-2.
It is the second New Haven semifinal in three years for Kirilenko, who lost to Nadia Petrova in 2010.
In the other half of the draw, second-seeded Petra Kvitova of the Czech Republic was scheduled to play her countrywoman and good friend Lucie Safarova Thursday night. The winner would play the winner of the late match between Sara Errani of Italy and Marion Bartoli of France.