World number one Caroline Wozniacki moved into the quarter-finals of the Qatar Open with a 6-3, 6-2 win over Russian Nadia Petrova but third seed Francesca Schiavone was upset by China's Peng Shuai on Wednesday.
Second seed Vera Zvonareva also secured a spot in the last eight with a 6-1, 6-2 win over Slovakia's Dominika Cibulkova, while fifth seed and former world number one Jelena Jankovic of Serbia thrashed India's Sania Mirza 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 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 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, who beat Wozniacki to reach the final of the Australia Open last month, was upset 6-2, 6-1 by Czech Klara Zakopalova, while France's Marion Bartoli eased past Israel's Shahar Peer 6-1, 6-0.