Vietnam put on a strong performance in a game where their opponents Malaysia did not have many options for players, with four infected with Covid-19 and one injured.
Nguyen Quang Hai made a thunderous strike with his left foot from Phan Van Duc's pass and opened the score for Vietnam in the 31st minute.
He helped double the score for Vietnam five minutes later with a backheel pass to Nguyen Cong Phuong, who dribbled past two Malaysia defenders before finishing.
With 15 minutes left, Vietnam started taking key players off the field to preserve their stamina for the next game.
But the remainders continued to put pressure on Malaysia and scored the third goal.
When Malaysia lost the ball in the midfield in the 89th minute, it was taken by Nguyen Hoang Duc, who is playing at AFF Cup for the first time. He easily dribbled past the defense line before shooting from outside the box into the left corner.
Vietnam's next game will be against Indonesia on Wednesday.