Azarenka, Sharapova reach China Open semifinals

"I thought we played a high level of tennis the first set and a half, and even though the score line was 6-0, 3-0, there were many games that went to deuce," Sharapova said. "She had a few break points and long games on her serve.

"I actually didn't see much of her injury. I was surprised she called the trainer and even more so when she retired quickly after that."

Sharapova has not dropped a set at the China Open. The French Open champion will next face seventh-seeded Li Na of China, who beat third-seeded Agnieszka Radwanska of Poland 6-4, 6-2.

Azarenka, who won the Australian Open this year, converted all six break points she earned and will next play either ninth-seeded Marion Bartoli of France or Carla Suarez Navarro of Spain.

"I felt like I was playing well, and that's what gave me an advantage to go and play and have that score line after the match, but it wasn't easy," Azarenka said. "Sometimes it's important to stay tough and have that concentration to make sure that you can win every ball and every point."