She finished the 82.2-km race held in Rayong province - about 140km to the southeast of Bangkok - first with a time of 1 hour 58.48 minutes.
Her closest competitors, Maneephan Jutatip of Thailand and Na Ahreum of the Republic of Korea, finished second and third, respectively, but were no match for the exceptional That.
The tournament taking place from April 8-10 attracted 11 Asian teams and clubs who have been competing in three races. The final race with a length of 89km will be held on April 10.
The Vietnamese team joins the tournament with five riders – Nguyen Thi That, Nguyen Thi Thi, Nguyen Thi Thu Mai, Bui Thi Quynh and Lam Thi Kim Ngan.
