The Thais were seeking revenge after losing 1-0 to the Vietnamese in the SEA Games final in Hanoi last month.
However, the match got off to a bad start for Thailand when Phan Tuấn Tài struck in the 1st minute to give Vietnam the lead. The Thais then levelled the score before half-time when Ben Davis, who plays for Oxford United in England, found the back of the net in the 34th minute.
Vietnam showed the confidence gained from their SEA Games gold medal after the break, taking the lead again with a goal from Nguyễn Văn Tùng in the 73rd minute.
But Thailand refused to be humbled for a second time by their fierce regional rivals, as striker Suphanat Mueanta swooped to score the equaliser in the 91st minute.
In the other Group C game, reigning champions South Korea crushed Malaysia 4-1.
Thailand will take on Malaysia in their second game of the tournament at Bunyodkor Stadium on Sunday at 10pm.