Amelie Mauresmo rallied to win a 20-point first-set tiebreaker and a 7-6 (9), 2-6, 6-3 quarterfinal over top-seeded Svetlana Kuznetsova at the Pilot Pen tennis tournament on Thursday night.

Mauresmo started off slowly, losing the first three games of the match. But she broke Kuznetsova in the seventh game of the set to force the tiebreaker and then survived five set points.

"I gave her chances to come back," Kuznetsova said. "She didn't have many possibilities to play. I let her come back into the match. She started to play very well."

Kuznetsova easily won the second set, but Mauresmo went up 4-2 in the third, then battled back from three break points on her own serve.

"I was just going for it, trying to be aggressive," Mauresmo said. "Not too much panicking."

The 30-year old came into this tournament ranked 18th in the world and seeded eighth. But it's a tournament in which she has flourished, reaching the semifinals for the second consecutive year, and the fourth time in nine tries.

"Just before the Open, I start to really play better, feel good physically, try to find a few things in my game," she said.

Kuznetsova became the second top seed to fall, after Sam Querrey used 15 aces to beat Nikolay Davydenko 6-3, 3-6, 6-4 in the men's draw earlier in the day.

Querrey trailed 15-40 at 4-all in the third set. From there, he finished off Davydenko by taking eight straight points, including two aces for a 5-4 lead before breaking him at love.

"I just took a couple deep breaths and just really focused on my first serve and fortunately hit two big first serves in there," he said. "You see that a lot when you save break points, that next game a lot of times you see guys go ahead and convert the break, that's kind of what happened."

Querrey, who will head into the U.S. Open as the second-highest ranked American man, opened the match with two aces, won eight consecutive points and was up 3-0 early. His serve reached 135 mph, but he also mixed things up, going wide and times and at others spinning serves into Davydenko's body. He won 81 percent of his first-serve points.

"I have no chance because (of his) first serve," Davydenko said.

The Russian needed a trainer to look at his right wrist midway through the match. He said it became sore from the force of Querrey's serves hitting his racket.

Second-seed Fernando Verdasco had no problems in his quarterfinal, ousting Jurgen Melzer in straight sets 6-3, 6-1.

He will play Igor Andreev in the semifinals. Andreev beat Leonardo Mayer 6-4, 6-7 (4), 6-3, to reach the semifinals for the first time after four quarterfinal appearances in New Haven.

"I had a very good chance to finish the match with two match points in the second set, and I was serving for the match and I couldn't close it," he said. "Then after all this, you just try not to think too much what happened and keep going. I'm happy that I won third set."

Defending women's champion Caroline Wozniacki had a much easier time, beating Virginie Razzano in straight sets 6-4, 6-3.

Wozniacki seemed to have a harder time with a bee, which chased her around the court during the fourth game of the second set.

"It just kept attacking me," she said. "I was trying to, you know, hit it with the racket, but still it didn't give up," she said. "It kind of felt like, you know, my opponent didn't want it to give up in the match; the bee didn't want to give up either."

Wozniacki will play Flavia Pennetta in Friday's semifinals. Pennetta beat qualifier Magdalena Rybarikova of Slovakia 6-2, 6-2.

Pennetta said she's happy with her play in New Haven, but is not concerned about winning this tournament.

"I just look to be prepared for the Open," she said. "This is my first important thing for me is to just get there and be prepared for a fight."

Elena Vesnina earned the first spot in the women's semifinals, beating Anna Chakvetadze 6-1, 7-5. It was Vesnina's first win against Chakvetadze in six attempts.

"She's not playing like she was playing a few years ago," Vesnina said. "If you will compare, she's a bit down right now."

Chakvetadze had problems with her service game, missing on 50 percent of her first serves.

Vesnina will play Mauresmo on Friday night.