CHINA'S leading woman triathlete Zeng Xiao has scotched allegations that the mainland athletes take performance-enhancing drugs to excel in sports. Zeng, the 1992 Asian women's junior champion, is in Hong Kong with five other mainland triathletes for the Puma International Sprint Triathlon at Tai Po on Sunday. ''It is unfair to say we [the Chinese] are on drugs when we do well in sports,'' said Zeng. ''We win with our true ability. It is undignified to win by cheating.'' The 20-year-old from Guangdong is expected to give Hong Kong short-course specialist Ruth Hunt a strong challenge for the $4,000 first prize. Zeng was running third at the Asian Championships in Tienjin two months ago when she collapsed with 400 metres to go. She should benefit from the reduction to the sprint course from the Olympic distance. The sprint - comprising a 750-metre swim, 20-kilometre bike ride and a five-kilometre run - is exactly half the Olympic distance. Zeng, who spends six to eight hours a day training, blamed herself for her failure in Tienjin. She said she had not trained hard enough in the run-up to the event. Hunt tipped Zeng and teammate Sue Ross as her strongest rivals, but warned that Indian 16-year-old Kapadia had the ability to pull off an upset. ''Zeng and Kapadia are very good swimmers and it won't be easy catching them,'' said 37-year-old Hunt. ''Besides, I'm better on the Olympic course.'' Local number one Ian Rayson stands out in the men's division and his main challengers are likely to be fellow-Hong Kong international Con O'Kelly and Chinese ace Quo Qingshan.