Vietnam took the lead in the third minute with an opener by Hoang Quoc Viet, who doubled the score with a long-range shot in the 31st minute.
The goal difference was brought to three just before half-time following a finish from a narrow angle by Khuat Van Khang.
In the early minutes of the second half, the score was narrowed to 3-1 with a goal by Temulen, raising Mongolia’s hopes of earning points.
But such hopes soon faded away when Nguyen Hoang extended Vietnam’s lead following a pass from Minh Trong in the 64th minute.
Mongolia defeated Vietnam’s keeper Quan Van Chuan once more in the extra time, but it was not enough to change the outcome of the match.
The other match of Group B between Iran and Saudi Arabia ended in a goalless draw. Vietnam are scheduled to meet Iran and Saudi Arabia on September 21 and 24, respectively.
