Second seed Petra Kvitova and reigning four- time champion Caroline Wozniacki were easy quarterfinal winners Thursday at the $637,000 New Haven Open at Yale, a final U.S. Open tune-up.

Kvitova, last year's Wimbledon champion, downed eighth-seeded fellow Czech Lucie Safarova, 6-3, 6-3. Kvitova clinched the U.S. Open series title. If she wins the U.S. Open, she will get a $1 million bonus on top of the prize money from the final major of the year. A runner-up finish would earn her $500,000.

Wozniacki, the third-seeded former world No. 1 star improved to 20-0 lifetime in New Haven with a 70-minute 6-2, 6-1 dismantling of sixth-seeded Slovak Dominika Cibulkova on the hardcourts at the Connecticut Tennis Center at Yale.

The Danish star beat Czech Petra Cetkovska in last year's New Haven finale.

The 2009 U.S. Open runner-up Wozniacki's semifinal opponent on Friday will be seventh-seeded Russian Maria Kirilenko, who flattened Belarusian qualifier Olga Govortsova 6-1, 6-2 in 1 hour, 23 minutes. Kirilenko lost to world No. 1 Victoria Azarenka in the bronze-medal match at the London Olympic Games earlier this month.

In the final match of the night, fourth-seeded Italian Sara Errani, this year's French Open runner-up, downed former Wimbledon runner-up and fifth- seeded Frenchwoman Marion Bartoli, 6-4, 6-2.

The 2012 New Haven champion will collect $107,000.