Top-ranked Victoria Azarenka and No. 2 Maria Sharapova advanced to the China Open semifinals on Friday.
Azarenka defeated Romina Oprandi of Switzerland 6-2, 6-0, and Sharapova beat sixth-seeded Angelique Kerber when the German retired with a right foot injury while trailing 6-0, 3-0.
''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.''
In the men's quarterfinals, third-seeded Jo-Wilfried Tsonga of France defeated Mikhail Yozhny of Russia 6-3, 6-2. Tsonga, who had a walkover in the third round, had seven aces and saved both break points he gave away.
''I think it was a good thing because I played three sets the day before,'' Tsonga said. ''For me it's good to have some rest.''
Unseeded Florian Mayer also reached the semifinals when he beat Chinese wild-card Zhang Ze 6-3, 6-4.
Tsonga will next play either Sam Querrey of the United States or Feliciano Lopez of Spain. Mayer will take on either top-seeded Novak Djokovic of Serbia or Jurgen Melzer of Austria.
