In the men's Group A match at the National Stadium, Vietnam virtually erased any Malaysian hopes to make the semfinals with a 3-1 victory.
All goals were scored in the first half, while striker Mohd Zaquan Adha Abdul Razak was flashed the red card towards the end of the match.
Vietnam had taken a two goal lead before Malaysia pulled back one, but through the courtesy of an own goal by Vo Hoang Quang.
Earlier Vietnam took the lead through a penalty goal by Phan Thanh Binh in the 13th minute after a handball in the box, before Mai Toen Thanh made it 2-0 in the 25th minute.
Vietnam undeterred by giving away a "gift goal" to Malaysia, went to score their third goal through Nguyen Troang Hoang second before the end of the first half.
Vietnam, who had in the opening match against Thailand drew 1-1, had defeated Timor Leste 4-0 on Saturday.
With this win, Vietnam have seven points and play their final Group match against Cambodia only on Friday.
Malaysia, on the other hand have only three points from two matches - after their opening 11-0 win over Timor Leste.
Malaysia play Cambodia on tomorrow (Tuesday) and cannot afford anything less than a win.
The only way Malaysia now have a chance to make the semifinals is to beat Cambodia and Thailand in their final match on Friday.
Indeed a tall order and losing to Vietnam has virtually closed the doors of a semifinals berth on them.
Thailand, on the other hand after their 1-1 draw to Vietnam in their opening match, went on to beat Cambodia 4-0 for a total of four points.
Thailand play Timor Leste tomorrow,
There was further humiliation hurled at Malaysia, when Vietnam sent the Malaysian women packing with a 8-0 win. The second defeat comes after an earlier embarrassment 14-0 defeat at the hands of Thailand.