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 quarter-finals. 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 quarter-finals. 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."

Wozniak downed at Texas Open

Third-seeded Roberta Vinci advanced to the Texas Open semifinals Thursday, beating seventh-seeded Chanelle Scheepers of South Africa 7-6 (1), 6-2.

Vinci, from Italy, will face the winner of a night match between sixth-seeded Peng Shuai and Bojana Jovanovski.

Australia's Casey Dellacqua also advanced, topping Aleksandra Wozniak 6-4, 6-4. In the other quarterfinal, second-seeded Jelena Jankovic faced eighth-seeded Sorana Cirstea.

Winston-Salem Open

Andy Roddick was eliminated from the Winston-Salem Open on Wednesday, losing a third-round match to Belgium's Steve Darcis in straight sets.

The fifth-seeded Roddick, a former world No. 1 player now ranked 21st, fell to the 81st-ranked Darcis 7-6 (8-6), 7-6 (7-3) in the final hard-court tournament before next week's U.S. Open in Flushing Meadow, N.Y.

"I did not expect this," Darcis said in his heavily-accented English. "When I came here, I was not playing so good. But I had two good first matches, and here I play very good tennis. I served very good, and I tried to be aggressive when I could.

"OK, Andy didn't play his best tennis, but for me it's a great win, especially before the U.S. Open."

Roddick had 13 aces, but the 2003 U.S. Open champion struggled to find consistency with his ground strokes and Darcis' short game, whose drop shots caught Roddick flat-footed several times.

Roddick's frustration was evident during Wednesday's match — he smashed his racket after losing the first set, and argued with chair umpire Carlos Bernardes on a let serve call early in the second.

"I served OK, but I didn't return too well and I wasn't hitting the ball clean out there today," said Roddick, who had beaten Darcis in two previous meetings. "If I don't lose serve, I should do fine, and I didn't. That just speaks to how far off the rest of my game was today."

Other winners in the third round Wednesday included fourth-seeded Alexandr Dolgopolov of the Ukraine and seventh-seeded Sam Querrey. Dolgopolov beat 14th-seeded David Nalbandian of Argentina 6-3, 6-4, and Querrey downed ninth-seeded Feliciano Lopez of Spain 6-3, 6-4.

Defending champion John Isner overcame two rain delays to advance in straight sets.

The third-seeded Isner, ranked 10th in the world, needed only 71 minutes to beat 13th-seeded Jurgen Melzer of Austria 6-4, 6-3 in the third round at the Wake Forest Tennis Complex.

Top-seeded Jo-Wilfried Tsonga of France also advanced to the quarters along with second-seeded Tomas Berdych of the Czech Republic, fourth-seeded Alexandr Dolgopolov of the Ukraine, sixth-seeded Marcel Granollers of Spain, seventh-seeded Sam Querrey and Belgium's David Goffin.

Tsonga defeated Sergiy Stakhowsky of the Ukraine 7-6 (7-1), 6-4; Berdych downed Finland's Jarkko Nieminen 6-3, 6-2; Dolgopolov beat No. 14 David Nalbandian of Argentina 6-3, 6-4; Granollers rallied to beat Latvia's Ernests Gulbis 4-6, 6-3, 6-2; Querrey edged ninth-seeded Feliciano Lopez of Spain 6-3, 6-4; and Goffin downed Poland's Lukasz Kubot 6-3, 1-6, 7-6 (7-5).