Chau Ngoc Quang capitalised on a defensive error to score in the 11th minute.
Van Vi doubled the lead just before half-time and added his second early in the second half.
Hai Long scored the fourth in the 63rd minute, while Quang Hai sealed the win with a volley in the 83rd minute.
With this strong start, Vietnam look ahead to their key match against Malaysia on June 10.
Vietnam, are in Group F with Laos, Malaysia and Nepal.
