Khairul Amri's 82nd minute wonder strike cancelled out Pipat Thonkanya's first-half opener and restored defending champions Singapore's one-goal advantage they held from the first leg.
''It was a great game, Singapore and Thailand are the best teams in the region and we achieved what we had to -- we knew we had to score a goal,'' Singapore coach Raddy Avramovich smiled afterwards.
Demonised four days ago for a petulant walk-off protest against a penalty awarded against them on Wednesday, Thailand's soccer redemption was almost absolute in Bangkok when they carried the game to Singapore, looking the more stylish and stronger side on a feverish night of action.
Thirty thousand Thai fans had rejoiced when Pipat took a flicked pass from fellow striker Datsakorn Thonglao on his head, nodded it up into the air and acrobatically thumped a volley past the lunging Lionel Lewis in the Singapore goal to level the scores on aggregate as the first half wound down.
The Thais spurned a number of chances to nose ahead in the second half and were made to pay when Amri collected the ball in the 82nd minute.
The home defenders held off as he twisted and turned and he finally released a thunderous shot from the edge of the penalty area which bulged the back of the net before Thai keeper Kittisak Rawangpa could move.
Thailand are the only other nation to win the championships, formerly the Tiger Cup, also three times.
REUTERS SAM RAI2017