BEIJING - Olympic singles and doubles champion Zhang Yining failed to reverse her struggling form as she lost to a former teammate for the fourth time on Saturday.

Jiang Huajun, playing for the Hong Kong team, beat Zhang 9-11, 11-9, 11-7, 11-6, 8-11, 11-5 in the women's third round of the Japan Open table tennis tournament in Chiba.

It was Jiang's fourth win over the more heralded rival since the 2005 Qatar Open, 2006 Kuwait Open and 2007 Croatia Open.

Zhang has been battling a poor form and nagging injuries this year, which also saw her lose in the straight sets to eventual champion Guo Yue of China in the Zagreb world championships in May.

"Zhang Yining isn't in form," her national team coach Li Sun. "She has to work harder if she wants to defend her crowns in the 2008 Beijing Olympics."

Li said threats to the Chinese women's team in the 2008 Olympics could come from outside the Chinese mainland.

"Hong Kong's women players are quite strong," said Li, who used to coach Jiang in the Chinese team before she moved to Hong Kong.

Beijing has churned out more table tennis expatriates than any Chinese cities. Zhu Fang (Spain), Li Jia Wei (Singapore), Yang Zi (Singapore), Zhang Xueling (Singapore), Wu Xue (Dominican Republic), Li Qiangbing (Austria) and Wang Chen (United States) are all from the Chinese capital.

The women's game of the 2007 European championships was dominated by former Chinese. Liu Jia failed to defend her singles honor while the 34-year-old Li Jiao of the Netherlands downed the 44-year-old Ni Xia Lian of Luxembourg in the final.

The Chinese team, which has lost only one world individual title in the new millennium, sees Singapore as another major threat.

All of the six-member Singapore team came from China. Its women' s players Li Jia Wei, Wang Yue Gu and Sun Bei Bei are ranked 7th, 8th and 17th in the world.

The top ranked Singaporean men are Gao Ning and Yang Zi.

Singapore is coached by another expat Chinese Liu Guodong, whose brother Liu Guoliang heads the Chinese men's team.

Li Sun's kid sister Li Jun now plays for Japan and another Chinese national team coach Li Xiaodong is the father of Li Qiangbing, who plays for Austria.

Qi Baohua, the elder sister of Qi Baoxiang, who coaches the Chinese second-string women's team, used to play for Hong Kong in the 1990s.

A dozen of Chinese coaches are advising foreign teams. Better known among them are New Zealand chief Li Chunli, England head coach Liu Jiayi, Wang Dayong, the mentor of Belgium's former world No. 1 Jean-Michel Saive, and Liu Yanjun, who guided Liu Jia to the European singles championship in 2005.