World number one Caroline Wozniacki [ Images ] moved into the quarter-finals of the Qatar Open with a 6-3, 6-2 win over Russian Nadia Petrova [ Images ] but third seed Francesca Schiavone was upset by China's Peng Shuai [ Images ] on Wednesday.

Second seed Vera Zvonareva [ Images ] also secured a spot in the last eight with a 6-1, 6-2 win over Slovakia's Dominika Cibulkova [ Images ], while fifth seed and former world number one Jelena Jankovic [ Images ] of Serbia thrashed India's [ Images ] Sania Mirza [ Images ] 6-0, 6-1.

"There's a lot of good players here, so it's not easy to win," said Dane Wozniacki, who will meet Italian Flavia Pennetta [ Images ] in the last eight on Thursday.

"It's not going to be easy tomorrow, but I'm looking forward to it," she added.

French Open [ Images ] champion Schiavone had a less memorable day with Chinese qualifier Peng in top form on her way to a 7-5, 6-3 victory.

"I missed a lot of easy balls. I should take some days off perhaps, but there is no time," the Italian said.

Peng's compatriot Li Na [ Images ], who beat Wozniacki to reach the final of the Australia [ Images ] Open last month, was upset 6-2, 6-1 by Czech Klara Zakopalova, while France's [ Images ] Marion Bartoli [ Images ] eased past Israel's Shahar Peer 6-1, 6-0.