With the aggregate score level at 1-1 from the first leg, Thailand only needed a goalless draw against the tournament’s defending champions to progress to the final on away goals.
Their task was made easier, however, when Malaysia were reduced to 10 men towards the end of a scrappy first half in which both sides struggled to impose themselves on a bumpy pitch at Supachalasai Stadium.
Malaysia defender Mohamad Fadhli was given his marching orders in the 43rd minute after receiving a second yellow card following an off-the-ball exchange of words with Datsakorn Thonglao, who also was booked for his role in the incident.
With the advantage, Thailand took control of the second half and went into the lead when Dangda slotted the ball home in the 60th minute for his fifth goal of the tournament, following a defensive error by Amar bin Rohidan.
Teerathon ensured a spot in the final five minutes later when he knocked in a rebound from a free kick that the Malaysia keeper failed to hold.
Thailand will travel to Singapore for the first leg of the final Wednesday (Dec 19), with the return in Bangkok on Saturday, Dec 22.