Midfielder Tien Long and striker Nguyen The Hung scored for Vietnam after the Cambodian side scored an opener just three minutes after the starting.
The Vietnamese players also missed a number of chances, as their front-line players either missed shots or were denied by the Cambodian goalkeeper.
With three points from the first match, Vietnam temporally top Group B while Cambodia sit at the bottom.
In the next matches, Vietnam will meet Brunei and Cambodia will face the Philippines tomorrow.
In today’s action, hosts Thailand will face Indonesia, Laos will take on Myanmar and Singapore will play Australia.