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.

Winston Salem Open

Defending champion John Isner and top-seeded Jo-Wilfried Tsonga had straight-sets victories Thursday night to set up a semifinal match in the Winston-Salem Open.

Second-seeded Tomas Berdych and seventh-seeded Sam Querrey also won their quarterfinal matches at the Wake Forest Tennis Complex in the final hard-court tournament before the U.S. Open.

Isner had 21 aces in beating David Goffin 7-6 (7-5), 6-3, while the sixth-ranked Tsonga needed only 53 minutes to dispatch sixth-seeded Marcel Granollers 6-1, 6-2.

Berdych, ranked seventh in the world, rallied to beat Steve Darcis 4-6, 6-2, 6-0, and Querrey topped fourth-seeded Alexandr Dolgopolov 7-5, 4-6, 7-6 (7-3).

Isner, born in nearby Greensboro, N.C., had 12 aces in the first set against Goffin, who saved four break points in the set to force the tiebreaker. But Isner had four aces in the tiebreaker, and got a key break on the seventh point to get the advantage. Isner then broke Goffin's serve in the fifth game of the second set, and closed out the set and match with another service break.

"I was pressing a little bit in that first set," said Isner, 2-1 against Tsonga, including a Davis Cup victory last April. "I was waiting for him to lose the set or make a mistake on a big point rather than me going after the ball. But I was happy with the way I played in the tiebreaker, and I played much better in the second set."

Tsonga, the highest-ranked player in the field at No. 6, had little trouble dealing with Granollers, breaking his first two serve attempts in the opening set, and adding two more service breaks in the second.

"I played well," Tsonga said. "I was into the match from the beginning and played good tennis. I don't know if he played his best tennis, I think he was a bit injured. But I played good tennis."

While Berdych's run of games held on serve ended at 29 with a pair of breaks in the first set, he had 10 aces and broke Darcis' serve seven times.

That included a run of six consecutive breaks over the second and third sets, and Berdych won the last nine games to advance to the semifinals for the third time this season.

"He was playing really smart, so I needed to change something," Berdych said. "I stepped a little bit closer to the baseline, and started to hit the ball a little faster. It changed the whole rhythm."

Querrey had 20 aces against Dolgopolov, who also had his serve broken twice in the first set. But the Ukrainian got a key service break in the second set to even the match, and kept Querrey scrambling in the third set.

However, Querrey got two break points in the tiebreaker to go up 5-1, and closed out the match with an overhead winner for his first win in three tries against Dolgopolov.

"It seemed that things just changed dramatically in the tiebreaker," said Querrey, the winner in Los Angeles last month. "It feels good to get the win today, but the matches are going to get tougher. I just going to have to play better if I want to keep winning."