The Vietnamese beat their Malaysian counterparts 2-1 on Sunday in the first-leg at Shah Alam Stadium.
The visitors were rocked by an early penalty by Safiq Rahim but came back with goals from Vo Huy Toan and Nguyen Van Quyet for the win.
"The players did very well and did not panic after conceding the first goal," said Vietnam coach Toshiya Miura.
Vietnam captain Le Cong Vinh echoed Miura's caution about thinking the tie has been won, saying the match at the Shah Alam Stadium was "only the first-half".
"We need to concentrate and make sure we finish the job in Hanoi," he added.
The second leg will take place at My Dinh Stadium on Thursday at 07H00 local time. The winners will face either Thailand or Philippines in the final later this month.