Mano Polking's side won for the second game in a row to top the five-team Group A standings alongside Indonesia, who threashed Brunei 7-0.
Teerasil headed in Theeraton Boonmatan's free kick in the third minute at Thammasat Stadium on the outskirts of Bangkok to give the Thais the perfect start against a Philippines side who had won one and lost one of their opening two games.
The former Sanfrecce Hiroshima striker doubled his side's advantage from the penalty spot with four minutes remaining in the half before turning provider in the 57th minute, setting up Adisak Kraisorn for Thailand's third.
Suphanan Bureerat stabbed in the fourth six minutes later to complete the rout.
Earlier, Indonesia crushed 10-man Brunei, who collapsed after Alinur Jufri's 38th-minute sending-off for a second bookable offence in Kuala Lumpur.
Shin Tae-yong's side, who finished as runners-up in last year's competition, led by a 20th-minute goal from Syahrian Abimanyu when Alinur was dismissed, prompting a flurry of goals.
Dendi Sulistyawan doubled the advantage before second-half goals from Egy Maulana, Ilija Spasojevic, Ramadhan Sananta, Marc Klok and Yance Sayuri completed Indonesia's second win in a row having also beaten Cambodia.
Thailand lead the group on goal difference from Indonesia, both teams on six points. Cambodia are third on three points, level with the Philippines who have played one game more.
Brunei are bottom of the group with zero points from three matches.
The group phase of the Asean Championship will continue until January 3 with the top two in each group advancing to the knockout rounds.
The semi-finals will be played on a home-and-away basis on January 6 and 9 with the final on January 13 and 16.
