YOKOHAMA, Japan (AFP) ? 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 fourth-ranked opponent 11-5, 11-6, 13-11, 11-4.

"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.

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.

Defending champion Guo Yue was stretched the distance before beating Jiang Huajun of Hong Kong 9-11, 13-11, 11-8, 8-11, 10-12, 11-4, 11-5.

South Korea's Dang Ye-Seo stormed back from match points down in the sixth game to beat Li Jiao of the Netherlands for a place against Li Xiaoxia.

In the men's competition, world number one Wang Hao outclassed Hong Kong's Jiang Tianyi, Ma Long breezed past Dimitrij Ovtcharov of Germany and three-time world champion Wang Liqin edged past Hong Kong's Tang Peng.

Olympic champion Ma Lin had to come back from 3-5 down in the final game to beat local hope Kenta Matsudaira 11-9, 11-7, 4-11, 13-11, 8-11, 8-11, 11-9.

The Chinese paddlers, who have monopolised 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 and went on to beat Zhang Jike and Mu Zi in the semi-finals.

In the final on Sunday, Hao and Chang will take on Li Ping and Cao Zhen, the winners over Zhang Chao and Yao Yan.