Luxembourg, Luxembourg (My Sportsbook) - U.S. Open champion Kim Clijsters was upset by Swiss lefthander Patty Schnyder in Thursday's second- round action at the $220,000 Luxembourg Open.

Schnyder surprised the second-seeded Clijsters in 6-4, 3-6, 7-6 (8-6) fashion at CK Sportcenter Kockelscheuer. The former world No. 1 Clijsters has won this event five times, with her last title here coming in 2005.

The 30-year-old Schnyder upended the two-time U.S. Open champion Clijsters in just under two hours, with the help of 11 double faults from the sturdy Belgian star.

Schnyder will face sixth-seeded German Sabine Lisicki in Friday's quarterfinals.

Meanwhile, fourth-seeded Slovakian Daniela Hantuchova held off Czech Lucie Hradecka 7-5, 3-6, 6-2 and hot fifth-seeded Belgian Yanina Wickmayer handled France's Alize Cornet 7-5, 7-6 (8-6). The U.S. Open semifinalist Wickmayer captured her second WTA Tour title of the year last week in Austria.

A mild Thursday upset came when Israeli Shahar Peer came back to best eighth- seeded Spaniard Carla Suarez Navarro 3-6, 6-3, 6-1.

One other second-round bout saw Slovenian Katarina Srebotnik overcome Luxembourg's own Anne Kremer 2-6, 6-4, 6-0.

The other quarters will pit Hantuchova against Peer, Wickmayer versus Belgian qualifier Kirsten Flipkens and Srebotnik against Swiss Timea Bacsinszky.

This week's titlist will claim $37,000.