The pair, who earlier this year claimed the Southeast Asian championship title and took silver at the Asian Championships, dominated the December 10 final with a time of 2 minutes and 6.487 seconds, overcoming a sluggish start to pull clear of the field.
They qualified comfortably in the morning heats with a time of 2:14.565 before producing a forceful performance in the medal race.
Hosts Thailand settled for silver through Orasa and Aphinya, who finished in 2:09.783, while Indonesia’s Aprilin and Sella earned bronze in 2:16.410.
The victory marks Viet Nam’s first gold of the Games, which run through December 20 in Bangkok, Chonburi and Songkhla.