Former champion Vera Zvonareva was an easy round winner Thursday at the $2.05 million Western & Southern Open, a U.S. Open Series event.

The second-seeded 2010 U.S. Open runner-up Zvonareva leveled Croatian qualifier Petra Martic 6-2, 6-2 in exactly one hour on the hardcourts at the Lindner Family Tennis Center.

Zvonareva, who titled here in 2006 and was the Cincinnati runner-up in 2004, will face Slovakian veteran Daniela Hantuchova in Friday's quarterfinals.

Last year's French Open runner-up Samantha Stosur upended this year's French Open champion Li Na in 6-4, 3-6, 6-4 fashion on Day 4. The 10th-seeded Aussie Stosur was last week's Toronto runner-up to Serena Williams, who pulled out of the draw here on Wednesday due to a foot problem.

The fifth-seeded Li, of China, was also this year's runner-up at the Australian Open in addition to her title at Roland Garros.

Another Thursday upset came when Hantuchova took out eighth-seeded French slugger Marion Bartoli 6-3, 5-7, 6-3.

The 2011 Cincinnati champion will collect $360,000.