Fourth seed Caroline Wozniacki eased into the quarter-finals on Wednesday, while top seed Sara Errani crashed out of the New Haven Open, the final tuneup for the US Open.
Petra Kvitova of the Czech Republic, who is seeded third, also booked her place in the quarter-finals of the US$690,000 hard-court tournament.
Four-time champion Wozniacki beat Italian qualifier Karin Knapp 6-1, 7-5, while last year’s French Open runner-up Errani was stunned by Russia’s Ekaterina Makarova 7-5, 6-1 at the Connecticut Tennis Center at Yale University.
“She’s not a comfortable player for me, as I had lost the last couple times we played,” Makarova said. “So today I was trying to be extra aggressive on my serve and go to the net. I also tried to attack her second serve.”
Former world No. 1 Wozniacki captured the New Haven title four years in a row from 2008 to 2011.
“I just wanted to try to get through this match in two sets, as I have had a bit of a cold the whole week and felt a little dizzy out there,” Wozniacki said. “She really stepped it up and started to play really well in the second set.”
Kvitova, who won the 2011 Wimbledon title, outlasted qualifier Alison Riske of the US 7-6 (7/5), 4-6, 6-3.
Errani’s loss makes it the first time in New Haven history that neither of the top two seeds advanced to the quarters. Second seed Angelique Kerber was eliminated on Tuesday.
Makarova’s quarter-final opponent is red-hot Romanian Simona Halep, who came from behind to beat Spaniard Carla Suarez Navarro 3-6, 6-4, 6-1.
The 21-year-old Halep is aiming for her fourth title in seven tournaments and is playing some of her best tennis heading into the US Open which begins Monday in New York.
Sixth-seeded wild-card Sloane Stephens of the US battled past Germany’s Julia Goerges 7-5, 2-6, 6-1 in the night match.