Oanh defended her title in the women’s 1,500m event after finishing with a time of 4min 14.98sec.
Her teammate Khuat Phuong Anh came second in 4:26.90, and Singapore representative Goh Chui Ling was third in 4:33.41.
It was Oanh’s third time winning this event at the SEA Games. This year she ran about three seconds faster than three years ago in the Philippines.
“I am happy to win the first gold medal for Vietnam in athletics. I hope that it will be a good start for the track-and-field team. Together we will complete and exceed our assigned target,” Oanh said.
She will continue to defend her second title women’s 5,000m event in the afternoon.
Her teammate Pham Thi Hong Le will also take part in the race.
Also in the afternoon, there are many other events organised.
National champion Tran Van Dang and Luong Duc Phuoc will defend Vietnam’s title in the men’s 1,500m. Reigning champion Duong Van Thai will not compete in this SEA Games as he has not performed at his peak recently.
The 400m mixed relay team will also compete to keep the title for Vietnam. At the Manila Games, the event was organised for the first time, and Vietnam came first and set a record of 3:19.50.
Debutante Ngan Ngoc Nghi will compete in the men’s 200m.
Nguyen Hoai Van will take part in the men’s javelin.
In the triple jump, Tran Van Dien and Nguyen Thuong Duc will test their skills.
Another gold for Vietnam belonged to wushu martial artist Duong Thuy Vi who succeeded in the women’s qiangshu (spear) event.
Vi topped the ranking with a 9.7-point performance, bagging her second title this Games after the first one in the jianshu (straight sword). Her teammate Nong Van Huu secured bronze in the men’s nanquan (southern boxing style).
In rowing, Pham Thi Hue won her title in the women's single sculls at the Games in the Thuy Nguyen Boat Racing Centre in Hai Phong City.
Duo Luong Thi Thao and Dinh Thi Hao won in the lightweight women's double sculls.
Teammates Tran Duong Nghia and Pham Manh Linh came second in the men’s pair event.