Caroline Wozniacki believes in treating the New Haven Open as much more than just a warm-up event for the U.S. Open.

The third-seeded Dane remained undefeated at the Connecticut Tennis Center on Wednesday, beating Sofia Arvidsson of Sweden 7-6 (4), 6-2.

Wozniacki is playing in the tournament for the fifth time and is the four-time defending champion. The victory Wednesday was her 19th without a loss at the tournament.

"I think I just have the same mentality every time I go into a match," Wozniacki said. "Out of respect for myself, the tournament and the opponent, I treat it as a match that I want to win."

Her chances for a fifth straight title improved Tuesday when top-seeded Agnieszka Radwanska retired in the second set of a lackluster performance against qualifier Olga Govortsova with a sore shoulder. Radwanska said she did not want to risk aggravating the injury going into the U.S. Open.

But another top player advanced Wednesday. Second-seeded Petra Kvitova of the Czech Republic earned a 6-2, 6-4 win over NCAA champion Nicole Gibbs.

The 2011 Wimbledon champion, the only Grand Slam winner in the New Haven field, is coming off a championship in Montreal and semifinal run in Cincinnati. She said the plan is to keep that roll going.

"I want to play a lot of matches here, and go for the U.S. Open with a good result," she said. "I want good matches in my bag."

The 19-year-old Gibbs, who is going into her junior year at Stanford, earned a spot in just her third WTA main draw through qualifying.

But this was in her second match this summer against a top player. She lost to Serena Williams earlier this season in the second round at Stanford.

"Having taking from that experience and this one tonight, I have more confidence that I can play at that level," she said.

She was able to come back from 4-1 down to tie Kvitova before world's fifth-ranked player put her away.

Kvitova will play one of her best friends, Lucie Safarova of the Czech Republic in the quarterfinals. Safarova beat Jie Zheng of China 6-4, 6-0.

Wozniacki had a tougher time in her match. She never trailed against Arvidsson, but dropped three straight games after being up 4-1 in the first set, and had to battle the rest of the way.

"I went a little bit down with my level, she went a little bit up and all of the sudden it was just a struggle to win that first set," Wozniacki said. "I'm just happy to be through. You don't always have to be playing your best tennis, but just win the most important points."

She will play Dominika Cibulkova in the quarterfinals. The 5-foot-3 Slovakian used a powerful forehand to beat Andrea Petkovic of Germany 6-4, 6-1.

"I'm compensating because I'm not so tall," she said. "I have developed the power, good swing in my arms. I use the power in my shots."

Petkovic, who is coming off injuries to her back and right ankle, was playing in her first tournament since April and just her fourth of the year.

"I'm quite satisfied because I didn't break my neck," she said. "That's a development from the last tournament. My strokes and my movement and my body is totally fine."