Nguyen Tran Duy Nhat easily won the Muay Thai gold medal in the men's 57kg category at the 2013 Asian Indoor & Martial Arts Games (AIMAG) in Incheon, South Korea on Tuesday.
With no Thai martial artists competing in this category, Duy Nhat breezed through to win all his five matches.
Nhat's gold and a gold in the women's 200m medley swimming event won by Nguyen Thi Anh Vien on Sunday put the Vietnamese delegation in fifth position at the event.
Bui Yen Ly and Phan Thi Ngoc Linh lost to their Thai rivals in the women's 51kg and 56kg Muay Thai events.
Tuesday was a disappointing day for the Vietnamese swimmers, partly because they spent their energy on too many events. Hoang Quy Phuoc came second in the men's 200m freestyle with a time of 1 minute 46 seconds, while Chinese gold medalist Mao Feilian did it in 1 minute 44.54 seconds.
Phuoc was not at his best because, less than 10 minutes earlier, he had fought hard without success in the men's 50m butterfly event .
The women's 200m medley gold medalist Anh Vien was in a similar situation. She put a lot of effort into the women's 200m freestyle and women's 200m backstroke finals, and could only finish fourth in the former and fifth in the latter.
Lam Quang Thanh, chief of the Vietnamese delegation, said it looked difficult now for Vietnamese athletes to win the targeted nine gold medals, but they would try to get at least seven.