Maria Sharapova through as Grand Slam champions fall

The Cincinnati Open claimed two more high-profile victims yesterday with grand slam champions Li Na and Petra Kvitova crashing out, while Russian pair Maria Sharapova and Vera Zvonareva crunched their opponents en route to the quarter-finals.

Li, China's first grand slam singles winner, was also beaten last week in Toronto by the Australian, who will meet Sharapova in the last eight.

Stosur is hitting a good run of form in the run-up to the U.S. Open, where she reached the quarter-finals last year.

"It would be the biggest title I've ever won," the 10th seed told reporters. "It would be fantastic but there is still a fair way to go before that can happen.

"I guess making the final last week gives me good confidence going into this week," added the 10th seed, who was runner-up in Toronto.

Wimbledon champion Kvitova fell to emerging German talent Andrea Petkovic, ranked 11th in the world, who enjoyed a 6-3 6-3 win in front of a smattering of fans on an outside court.

At the same time, on center court, Sharapova was making quick work of compatriot Svetlana Kuznetsova in a 6-2 6-3 victory.

"I felt really good considering I was playing a pretty tough opponent," said Sharapova. "We've had really tough matches in the past, usually three setters. So it was quite nice to get that win in two.

"She's someone who has a tremendous amount of experience and is a really solid player, always dangerous."

World number two Zvonareva crunched Croatian qualifier Petra Martic 6-2 6-2 and will face Slovak Daniela Hantuchova, who beat France's eighth-seeded Marion Bartoli 6-3 5-7 6-3..

Another Russian, Nadia Petrova, enjoyed a 6-3 6-3 victory over American teenager Christine McHale, who upset top seed Wozniacki in the second round.

Serbia's Jelena Jankovic twice failed to serve for the match but finally prevailed over Italy's Francesca Schiavone 6-3 5-7 6-4.

Jankovic looked in charge in the second set but allowed the Italian back into the encounter and yet the Serb recovered to go 5-1 up in the third, only for her focus to slip again.

"That took a lot out of me mentally and physically," said the Serb.

Jankovic will face China's Peng Shuai, who beat Israeli Shahar Peer in straight sets.