NEW HAVEN, Conn. (AP) Second-seeded defending champion Petra Kvitova rallied to beat Madison Keys 4-6 6-1, 6-2 on Wednesday night in the third round of the Connecticut Open.
''The conditions (without the humidity) were perfect for me, for sure,'' said Kvitova, who revealed several weeks ago that she has mononucleosis. ''I felt good and I didn't really have any troubles.''
The Czech player also won the event in 2012,
''I didn't really think I was in any trouble out there,'' Kvitova said. ''My only loss came on my serve in the first set, otherwise I thought I was kind of OK from my side.''
Kvitova bounced back with a strong second set, but was tested early in the third by Keys. Kvitova broke the Americans' serve to take a 3-2 lead, then overcame a 40-0 deficit to take the next game.
''She completely raised her level,'' Keys said. ''I had a couple chances here and there. I mean she played really well. It's tough when you have your break point and stuff like that, but she's hitting great shots and she's putting all the pressure on me.''
Kvitova will face seventh-seeded Agnieszka Radwanska of Poland in the quarterfinals. Radwanska beat France's Alize Cornet 6-4, 6-2.
''I'm just very happy to finish the match in two sets,'' Radwanska said. ''She's a great fighter, so I knew it was going to be a long match. She can really play everything and you can expect everything from her side.''
Fifth-seeded Karolina Pliskova of the Czech Republic topped Ukraine's Olga Savchuk 6-4, 6-1 in 52 minutes to set up a match against lucky-loser Lesia Tsurenko of the Ukraine. Tsurenko got into the field Sunday after top-seeded Simona Halep pulled out because of an injury.
With fourth-seeded Lucile Safarova advancing Tuesday, the Czech Republic has three players in the quarterfinals. Safarova will play Slovakia's Dominika Cibulkova.
Third-seeded Caroline Wozniacki of Denmark outlasted Italian qualifier Roberta Vinci 6-4, 6-7 (3-7), 7-6 (9-7) to advance in a tournament she has won four times (2008-11).
''She made it tricky out there with her slice and her flat forehand and mixing up the serve and stuff,'' Wozniacki said. ''The good thing is I am through and I get another chance tomorrow.''
Wozniacki saved three match points in the final-set tiebreaker and came back from a 7-6 hole to win.
''I just kept fighting,'' she said. ''That's the best thing I did today, and never give up.''
In addition to making early exits in her past three tournaments, Wozniacki came into the event battling calf and lower back issues.
''I haven't really been playing much late, so it's nice to get into that rhythm and just feel like I can improve every match,'' she said.
Wozniacki will play France's Caroline Garcia.