Former world No. 1 and 2010 runner-up Maria round Russian winners Thursday at the $2.05 million Western & Southern Open, a U.S. Open Series event.

The fourth-seeded Sharapova drilled 14th-seeded fellow Russian Svetlana Kuznetsova 6-2, 6-3, while 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.

The three-time major champion Sharapova was last year's Cincy runner-up to U.S. Open champ Kim Clijsters and this year's Wimbledon runner-up to Czech Petra Kvitova.

Sharapova will face tough Aussie Samantha Stosur in Friday's quarterfinals, while Zvonareva, who titled here in 2006 and was the Cincinnati runner-up in 2004, will take on Slovakian veteran Daniela Hantuchova.

Last year's French Open runner-up Stosur upended this year's French Open champion Li Na in 6-4, 3-6, 6-4 fashion on Day 4. The 10th-seeded 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 Roland Garros title.

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

Former top-10 player and 2008 Cincinnati champion Nadia Petrova of Russia pasted American teenager Christina McHale 6-3, 6-3. McHale stunned world No. 1 Caroline Wozniacki here on Wednesday.

The 2011 Cincinnati champion will collect $360,000.