As one of the title favourites, the two-time World Cup participants were considered much stronger than their rivals.
Nhan Gia Hung needed only three minutes to prove Vietnam's strength after consecutive attacks from the first whistle.
Hung took his ball in the box after a smart free kick on the left wing and had an easy opportunity with a close-range tap-in to open the scoring.
Timor Leste were on the back foot and goalkeeper Santos Gama did his good job to prevent Vietnamese pivots from scoring in the remainder of the first half.
Timor Leste replied three minutes after the restart as Fernandes broke through Vietnam's defence and passed the ball to Cesario Silvano Barreto in the box who netted with ease as former world top 10 goalkeeper Ho Van Y stood still and watched the ball go past him.
A minute later, Guterres nearly made it 2-1 for Timor Leste as his straight shot passed Y but he was denied by the left post.
Vietnam finally found their footing and scored three more goals in a rampaging second period.
Nguyen Manh Dung restored Vietnam’s advantage in the 25th minute, before Nguyen Thinh Phat scored a double in the 36th and 40th minutes for the win.
Hosts Thailand beat Brunei 13-0 to top the group's table.
In the next fixture on November 3, Vietnam will play Malaysia which rested in the first round and Timor Leste will face Brunei.
The regional championship feature nine teams, playing in a one-leg round robin group stage. The two top teams from each group will advance to the semi-finals, with the final scheduled for November 10.
