Huyen triumphed in her preferred event, the women's 400m. She finished with a time of 52.27sec.
During the first leg of the tournament, four days ago, she wasn't looking so strong, finishing in fifth position.
YuliyaRakhmanova of Kazakhstan topped the first leg of the event, followed byHuyen's teammate, Quach Thi Lan, running a solid 53.26s. For the secondleg, Quach Thi Lan came in fourth despite a better time of 52.75s.
Accordingto the head coach of the Vietnam team, Duong Duc Thuy, Huyen ran badlyin the first leg because of food poisoning but she came back and foundher form on June 25.
It is Huyen's first Asian title and the first gold for Vietnam in the women's 400m event.
Earlier,she pocketed a berth for the Brazil Olympics after an outstandingperformance at the recent Southeast Asian Games in Singapore.
Elsewhere in track, Tran Hue Hoa took silver in the women's triple jump with a result of 13.75m.
According to coach Nguyen Nam Nhan, Hoa's result was pretty good as it closely trailed the first place result.
Hoa, however, will have to work harder to beat a bar of 14.20m to qualify for the Olympic Games next year.
Vietnamese athletes competed in the men's 100m, 400m, 800m and women's 800m but failed to place.
The third and final leg will start June 29 in Chantaburi province.
The Grand Prix offers a total of 50,000 USD to the winners.-VNA