After playing aggressively for the first 10 minutes, the Filipina booters unraveled after the Thais were able to score the opening goal through a penalty kick in the 13th minute.
"Everything went downhill after that. My players became unsettled. We tried to get back in the second half but the damage had been done," said head coach Marlon Maro. "I would like to apologize to our countrymen that we started out this way."
Maro added things could have been different had the Philippines scored earlier, citing pointblank misses in the early going by Brenda Gayagoy, Rachel delos Reyes and Michaela Martinez.
"We will try to play our hearts out when we take on Myanmar tomorrow to stay in contention," he said referring to the crucial game against the Burmese at 6 p.m. Thursday.
Myanmar, banking on the hat-trick of star striker Mar Lin Win, dumped host Malaysia, 5-1, in the other Group A match.