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.