Top seed Victoria Azarenka and Maria Sharapova storm into semi-finals of China Open.

Azarenka comprehensively defeated Romina Oprandi of Switzerland 6-2, 6-0 while Sharapova did not have to try too hard against the German Angelique Kerber who retired hurt after a foot injury. Kerber was trailing 6-0, 3-0.

"I thought we played a high level of tennis the first set and a half, and even though the scoreline 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."

Azarenka , the Belarusian, has won four titles this year, including her first Grand Slam title at the Australian Open.

She will face the winner of the quarterfinal between Marion Bartoli of France and Carla Suarez Navarro of Spain in the semi-final Saturday.

She had withdrawn from her previous tournament in Tokya due to dizziness, but did not look at all troubled here.

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

Earlier in Thursday's game Azarenka had defeated Russian Elena Vesnina 6-3, 6-3 in straight sets to enter the quarterfinals while Sharapova beat Polona Hercog from Slovenia 6-0, 6-2.

While in the men's quarterfinals, the third-seeded French Jo-Wilfried Tsonga beat Russian Mikhail Yozhny 6-3, 6-2. Tsonga had seven aces and saved both break points.

Tsonga said: "I think it was a good thing because I played three sets the day before. For me it's good to have some rest."

Florian Mayer, the unseeded German, made it to the semi-finals as well. He comprehensively defeated the Chinese wild card entry Zhang Ze 6-3, 6-4.

Tsonga will now play against either Feliciano Lopez of Spain or Sam Querrey of the United States while Florian Mayer will face one of Jurgen Melzer of Austria or the top-seeded Novak Djokovic of Serbia.