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Madrid, Spain (Sports Network) - Defending champion Petra Kvitova was a stunning second-round upset victim Wednesday at the $5.190 million Madrid Open, a clay-court French Open tuneup.

The third-seeded Wimbledon titlist Kvitova was ousted by qualifier and fellow Czech Lucie Hradecka in easy 6-3, 6-2 fashion on the unusual blue clay at The Magic Box. Hradecka tallied three more service breaks (5-2) than the sluggish Kvitova to advance.

The lefthanded Kvitova topped current world No. 1 Victoria Azarenka in last year's marquee Madrid finale.

Meanwhile, fourth-seeded world No. 3 Agnieszka Radwanska avoided a second- round upset by leveling last week's Budapest champion and three-time 2012 WTA winner Sara Errani of Italy, 6-0, 6-1, in a mere 65 minutes on Day 5.

Two of last year's Grand Slam champions prevailed in third-round action Wednesday, as No. 5 seed Samantha Stosur of Australia whipped Czech Petra Cetkovska 6-3, 6-2 and No. 8 seed Li Na of China got past 12th-seeded rising German Angelique Kerber 7-5, 6-4. Stosur was last year's U.S. Open winner, while Li is the reigning French Open champ.

In some other second-round play, Ekaterina Makarova upended 16th-seeded fellow Russian Maria Kirilenko 6-4, 6-4 and quality Italian Roberta Vinci routed Belgian Yanina Wickmayer 6-1, 6-2.

In some more third-round play on Thursday, second-seeded former No. 1 Maria Sharapova will take on Czech Lucie Safarova, Radwanska will battle Vinci and sixth-seeded Dane Caroline Wozniacki should have her hands full with her ninth-seeded fellow former No. 1 Serena Williams, the 13-time major champion and 2011 U.S. Open runner-up to Stosur. Wozniacki was the Madrid runner-up in 2009.

This year's Madrid Open winner will earn $830,500.