Iran, who played a cautious game in the first half, scored just one goal through Ali Gholam Zadeh in the 30th minute to lead 1-0 at half time.
After the break, Iran started to play more aggressively and netted the ball four more times through Mohmmad Ghaderi (47th), substitute Alireza Asadabadi(62nd), Amir Khodamoradi (69th) and Ali Gholam Zadeh (72nd).
On the other hand, Vietnam started off brightly but surrendered after conceding the first goal and could never recovered.
Iran preferred to play a safe game and kept their citadel intact. They attacked the rival goal with long overhead passes to punch hole into the rival defence and succeeded in taking the lead in the 30th minute.
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Defender Ahmad Reza Jalali, who overlapped well on the left, send a high cross that beat rival defender and Allahyar Sayyad outsmart his marker as he leaped high to head the ball into the net.
Ghaderi then increased the lead soon after resumption in the 47th minute when he chested down a well directed lob from the right by Mohammad Sharifi before he dispatched the ball to the far corner of the net from inside the box.
Substitute Asadabadi sealed the contest in favour of Iran as he tapped the ball into the net after Ali Gholam Zadeh shot was blocked by keeper Huynh Huu Taun in the 62nd minute.