Thailand suffered a 2-0 defeat at the hands of Japan in their opening Group C match of the women's football competition at Bumi Sriwijaya Stadium yesterday.
Mana Iwabuchi and Yuka Momiki scored in the 33rd and 85th minutes as the Nadeshiko made a flying start to their Asian Games campaign.
Thailand will now need to beat Southeast Asian rivals Vietnam in their second group game on Sunday to keep alive their hopes of progressing.
The Nadeshiko, the 2011 world champions and current Asian titleholders, will conclude the group action against Vietnam next Tuesday.
The top two sides of Group C will qualify for the knockout stages.
Vietnam pipped Thailand on goal difference to win the gold medal at last year's SEA Games after a round-robin competition.
As expected, Japan put on a confident display that easily put the Thais to the sword.
After a dominant opening stage, Iwabuchi finally broke the deadlock to put the Nadeshiko 1-0 up eight minutes before the interval.
Thailand looked set to hold Japan to just one goal but Momiki ensured the tournament favourites got their second goal of the night with six minutes to go.
In Group A, South Korea defeated Taiwan 2-1. Jeon Ga-Eul (8th) and Jang Selgi (53rd) were on target for the Koreans, while Yu Hsiu-chin (74th) pulled one back for Taiwan. Hosts Indonesia overwhelmed the Maldives 6-0 in the other Group A game.
Group B comprises North Korea, China, Hong Kong and Tajikistan. The top three teams of Groups A and B advance to the knockout stages.
Like their male compatriots, the Chaba Kaew have never won a medal at the Asian Games. However, they made it to the 2015 Women's World Cup and have again qualified for the 2019 finals.