The Hai Phong City-raised athlete was also the first Vietnamese person to reach the world top three at the World Championships event last October.
In China, Thanh, 21, achieved a perfect jump in the women's horse vault to win the event with 14,700 points - her career best. She left in the dust title favourites former Olympic champion Hong Un-jong and teammate Ri Un-ha, both from North Korea, as well as China's Li Yiting, who just won a gold in the team's all-round event.
Head of the Gymnastics Department Nguyen Kim Lan was surprised by Thanh's performance, saying that she had excelled her previous record at the World Championships.
Thanh was the first Vietnamese gymnast to earn an official place in the London Olympics in August. She also dominated the 26th Southeast Asian Games last November in Indonesia with three gold medals.
In other events, Chinese gymnast Liu Rongbing continued to impress, claiming his third gold medal on the pommel horse. Liu, 21, who won the men's team and all-around titles on the opening day of the championships, earned the highest pommel horse score of 14.700 points.
His teammate Wu Liufang topped the women's uneven bar contest with 15.200 points. Then North Korean veteran Ri Se-gwang won the men's rings with 15.450 points.
The Asian tournament will conclude today with men's categories. Viet Nam will compete in the horse vault, parallel and rings events.
The Asian Gymnastics Union has registered the participation of 17 federations represented by 128 athletes, of whom 48 are women.
The event is an all around/team final and event final competition. This is the first time that North Korea participate after a two-year suspension.
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