Striker Nguyen Quang Hai scored two goals in the first half and Nguyen Trong Hoang and Huynh Quoc Anh each added one in the second to delight the home fans.
The victory gives Vietnam their first three points and makes the last round on October 28 more interesting as those matches will determine the winners of the competition.
"My boys played better today but I am not happy because the defence still left some spaces for the opposition to exploit," said Phan Thanh Hung, Vietnam's head coach.
The Laos manager Kokichi Kimura said that his team did not play well and he has a lot of work to do to improve their game.
It was a confident Laos who started the match brighter and had the first chances. However Vietnam were keen to make amends for their disappointing defeat at the hands of Turkmenistan two days ago, and they quickly found their rhythm.
Hai grabbed the game's opening goal when he beat the offside trap to collect a fine floating pass from Nguyen Vu Phong and stroked the ball into the net. He should have doubled his tally in the 27th minute, but wastefully fired wide.
He made no mistake five minutes later, doubling the score from the spot after Lao keeper had pulled Luong down in the penalty area.
Hung made two super substitutions in the second half, with attacker Hoang and winger Anh putting the game beyond doubt.
In the day's other fixtures, the Republic of Korea (RoK)'s U23 team trounced Turkmenistan 4-0 to lead the competition with six points from their two games.
A draw against Vietnam in the last match on October 21 is enough for the RoK to lift the trophy.