Neither side scored a goal until Kroekphon Arbram made use of Vietnamese goalkeeper Cao Van Binh’s mistake to put Thailand ahead with a header in the 72nd minute.
However, Vietnam earned an equaliser four minutes later with Khuat Van Khang’s decisive shot.
The score was maintained till the referee’s last whistle.
In another Group A match at the same time, hosts Indonesia stunned Myanmar 5-1, but they had to bid farewell to the tournament due to the 1-1 draw between Thailand and Vietnam.
After five group matches, Vietnam, Thailand and Indonesia all had 11 points, but Vietnam and Thailand finished first and second in Group A thanks to the goal difference of their head-to-head matches.
Rivals of Vietnam and Thailand in semi-final matches will show up after the Group B matches end.