The Vietnam team faced many difficulties as many of its important players were out with injuries.
U-21 Indonesia rapidly dominated the game from the starting whistle and opened the scoring in the 36th minute with a header from Miko Ardianto.
In the second half, Indonesia continued to control the game and stepped up pressure on the Vietnamese side, aiming to widen the scoring gap. It was not until the 74th minute that Andik Vermansyah made the goal that finalised the game at 2-0.
In the other semi-final match, hosts U-21 Brunei beat U-21 Myanmar 3-2 to secure their place in the finals.
U-19 Vietnam and U-21 Myanmar will share the third prize while hosts U-21 Brunei take on U-21 Indonesia in the finals at Sultan Hasannal Bolkiah Stadium tomorrow.
The Vietnamese team will gather again in August to prepare for the 2012 U-19 ASEAN Football Federation Championships.