Nguyen Van Tung headed the ball past Lao goalkeeper Seeamphone Sengsavang in the second minute to open the score at Prince stadium in Phnom Penh, Cambodia.
The defending champion then came close to extending their lead in the 16th minute when Le Van Do forced Sengsavang into a fine save from a set-piece situation.
A resilient Laos made it difficult for Viet Nam from there on and even came close to finding the equaliser in the 75th minute through Theo Klein's free-kick which rocked the crossbar.
Laos also created number of threatening opportunities with a view to find an equalizer but Vietnamese goalkeeper Quan Van Chuan produced excellent saves. He denied all of Laos' attempts.
Viet Nam, however, delivered the final blow in the closing stages of the game with substitute Nguyen Quoc Viet scoring with a close-range finish in the additional time.
Speaking with reporters after the match coach Philippe Troussier of Viet Nam said he was pleased with the victory although his team struggled through the match.
The French congratulated his players for the win and said the first match was always hard. It was harder for Viet Nam as they were reigning champion and under heavy pressure to defend their crown.
He said he was happy with two goals scored from live ball situation and Viet Nam was successfully kept their sheet clean.
Goalkeeper Chuan also attended the post-match briefing. He said Viet Nam made mistakes in the matches, giving Laos chances to threaten his box. These mistakes must be fixed prior to the next matches to ensure Viet Nam's positive results.
Viet Nam will face Singapore next on May 3, while Laos will aim to bounce back against Malaysia.
After the first round match, Thailand, who beat Singapore 3-1 in an early game on April 30, places on the top position of Group B. Viet Nam comes second, followed by Singapore, Malaysia and Laos.
In Group A activities on April 29, Cambodia delivered Timor Leste a 4-0 drubbing in one of the opening football matches of the SEA Games, while Indonesia dispatched the Philippines 3-0.
The host will face the Philippines on May 2 while Myanmar will see Timor Leste at the Olympic National Stadium. /.