The winning goals were scored by Pathompol Charoenrattanapirom and Supachok Sarachart at the 51st and 81st minutes, respectively.
Thailand, the five-time champion at the Asean Football Federation (AFF) Championships, will be playing against Myanmar next Saturday (December 11).
The 13th edition of the championship was originally scheduled to run from November 23 to December 31, 2020, but had to be postponed by a year due to the Covid-19 pandemic.
It is now being held in Singapore from December 5 to January 1.
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