Brunei's unusual tactic of playing a high defensive line backfired spectacularly as the speedy Vietnamese raced to a 3-0 lead before the half-time break, courtesy of goals from Vu Minh Tuan, Minh Tuan Ha and Le Van Thang.
Apart from a few long-range efforts Brunei were largely restricted to defensive duties in the first-half.
The game was effectively killed off eight minutes after the restart as Thang grabbed his second goal of the game to make it 4-0.
Despite the scoreline, Brunei hung on to their defensive tactic and were woefully punished as Tran Manh Dung, Mac Hong Quan and Phi Son Tran got themselves on the scoresheet to make it a resounding 7-0 for the night.
Brunei's Korean coach Kwon Oh Soon lamented the lack of preparation for his team's poor display.
"We lacked preparation for the SEA Games, our team has a lot of weaknesses, and there's a big gap between our players and Vietnamese players," admitted Kwon as he spoke to Goal after the match.
"They are professional players, but we hope in the next match we will get a better performance than today."
Vietnam's Hong Van Phuc on the other hand was delighted with his side's showing and was hopeful of making it through to the next round."The opening match is very important for our team," Hong told Goal.
"We couldn't get good form till 15 minutes in and we lost two or three chances to take the lead. We played long balls but it was not effective, so we changed our style of play. I hope we will reach the semi-final."
Vietnam next face Singapore on Tuesday. The Young Lions could only register a disappointing 1-1 result in their opening fixture against Laos who played with 10 men for almost the entirety of the match.
