Competing against strong contenders from China, Japan, and Kuwait, Oanh began in the seventh lane at the tournament on Saturday.
The SEA Games champion quickly rose to the occasion, taking the lead after one and a half laps and widening her gap from her competitors and the race progressed.
She crossed the finish line in 4 minutes and 15.55 seconds, smashing Truong Thanh Hang's national record of 4:23.04 set 14 years ago and outpacing her nearest rival, Japan's Goto Yume, by almost 50 meters and 4 seconds. Yume finished with a time of 4:19.29, while Akbayan Nurmamet of Kazakhstan placed third with a time of 4:21.29.
On February 10, Oanh competed in the women's 3,000m, the event that she had not competed in for years. She finished with a time of 9:18.41 which was much better than the result of 9:48.48, which brought her a bronze in the 2018 championship in Iran.
It is the third gold of Vietnam in this competition. The first two went to Hang in the women's 800m event in 2010 and Bui Thi Thu Thao in the women's long jump event in 2018.
It is also Oanh's first title in the Asian Indoor tournament. She bagged two bronzes in her first participation in 2018.
Minutes after Oanh's victory, another Vietnamese athlete, Nguyen Thi Huyen, secured a silver in the women's 400m event. The SEA Games champion finished second, clocking 54.67sec, just 0.6sec behind the winner Elina Mikhina of Kazakhstan.
SEA Games winner Luong Duc Phuoc took part in the men's 1,500m event. Despite his big effort, he placed ninth from 12 runners.
The top three were Kazuto Ilzawa of Japan, Mohammad Algarni and Musaab Adam Ali, both of Qatar.
The last Vietnamese competitor Nguyen Trung Cuong will compete in the men's 3,000m against 14 other runners.
Cuong is the champion and record holder of the National Sports Games 3,000m steeplechase.
The Asian Indoor Athletics Championships was held from February 10-12, with about 500 athletes from 31 countries and territories competing across 26 disciplines of running, throwing, jumping, and all-around events.
The Astana championships are the 10th edition of the tournament. The biennial event, organized by Asian Athletics Association, was canceled in 2020, while last year's event was pushed forward due to Covid-19.
In the 2018 championship, Vietnam ranked seventh with one gold and three bronzes.