YOKOHAMA: Chinese teenager Liu Shiwen upset fellow national and 2005 silver medallist Guo Yan to reach the women's singles quarter-finals at the world table tennis championships on Saturday.

The 18-year-old Liu, ranked 12th in the world, continued her run of flawless victories by taking the fourth round match without dropping a game against her 4th-ranked opponent.

"It was a tough game, because my opponent was also a Chinese. This is my first appearance in the world championships and I think I was able to play with a fresh feeling," said Liu.

Fellow Chinese Zhang Yining and Li Xiaoxia will both join Liu in the quarter-finals.

Beijing Olympic gold medallist and world number one Zhang brushed aside Krisztina Toth of Hungary to move another step closer to regaining the singles title she won in 2005.

"It was not a difficult match, but I played seriously. I can play better. A tough, real competition will start from now on. I'm going to prepare for tomorrow's match," said Zhang, 27.

"It was a bit hot here and I didn't feel comfortable, but I played each game carefully. I never lost my nerve even when I lost a point. I was calm throughout the match."

After beating her teammate Ding Ning, world silver medallist Li said she had been pleased with her performance.

"I played some 70 rallies in this match. I just returned everything hit at me. I feel good. It was a good game," she said.

Another Chinese, defending champion Guo Yue, was set to play Jiang Huajun of Hong Kong later in the day.

The Chinese paddlers, who have monopolized the honours in the previous two championships and swept the board at the Beijing Olympics, have already secured at least one title this year after the mixed-doubles semi finals became an all-Chinese affair.

Hao Shuai and Chang Chenchen eliminated the top-seeded Hong Kong pairing of Ko Lai-chak and Tie Yana to set up a match against Zhang Jike and Mu Zi.

The other semi-final will be played between Li Ping and Cao Zhen, and Zhang Chao and Yao Yan.