Jelena Jankovic and last year's runner-up Agnieszka Radwanska became the latest top seeds to tumble out of the China Open in Beijing.
Men's fifth seed Tomas Berdych also suffered an upset Monday against German qualifier Michael Berrer, and was followed out of the tournament by Fernando Verdasco, who lost 6-2, 7-5 to Germany's Philip Kohlschreiber.
Third-seeded Jankovic fell to fellow Serb Bojana Jovanovski 6-2, 2-6, 2-6, while Poland's sixth seed Radwanska lost out to unseeded German Angelique Kerber, who twice fought back from 5-4 down to record the 5-7, 7-6 (3), 7-5.
''It wasn't easy for me to play against her,'' Kerber said. ''We've known each other a long time. It was very hot out there but I just tried to take it one point at a time and play my tennis, being aggressive and putting pressure on her.''
Defending champion Svetlana Kuznetsova and fourth-seeded Sam Stosur both went out on Sunday, potentially easing Caroline Wozniacki's bid to become the top-ranked player in the world.
Wozniacki needs to reach the quarterfinals to replace Serena Williams as the No. 1.
China's hopes for a championship suffered a setback after Peng Shuai gave up a 6-1, 4-2 lead to lose against Italy's Sara Errani 1-6, 6-4, 6-1. Compatriot Li Na remains in the tournament after her first-round win on Sunday.
Second seed Vera Zvonareva kept her title hopes alive with a 6-4, 7-6 (6) win against fellow Russian and former No. 1 Dinara Safina.
On the men's side of the draw, Berrer battled back to beat Berdych 4-6, 7-5, 6-4, while Kohlschreiber saw off Verdasco with a convincing 6-2, 7-5 win.
American Mardy Fish fired 10 aces on his way to a 6-2, 7-6 (5) win against Janko Tipsarevic of Serbia.
Frenchman Gilles Simon also advanced with a 6-3, 3-6, 6-2 win over Sam Querrey of the United States.
No. 2-ranked Novak Djokovic of Serbia is defending his title in Beijing, while Andy Murray of Britain, Sweden's Robin Soderling and Nikolay Davydenko of Russia are also competing.
