Vietnam will play Australia, represented by their Under-20 squad, while Myanmar have to take on defending champions Thailand in the last four.
The more organised Vietnam scored early in the first half before adding three more goals after the break as Myanmar staged a late revival for the final scoreline at the Jaka Baring Stadium..
“It is good to score four wins from four matches,” said Vietnam head coach Mai Duc Chung. “Now we will look forward to playing against Australia in the semi-finals.”
Sealing top spot would have meant avoiding Thailand in the semi-finals and Vietnam took the lead 12 minutes into the game when a poor clearance by the Myanmar defence allowed Pham Hai Yen to stab home.
Vietnam widened their lead five minutes into the second half when Hai Yen made good of a cross from captain Huynh Nhu.
Five minutes later, Huynh Nhu found the back of the net with a well-taken free-kick as Myanmar then grabbed their first goal of the game through Win Theingi Tun with a 58th minute effort.
The game went into higher gear after that with Huynh Nhu again finishing in the 77th minute from Pham Hoang Quynh's cross.
Myanmar gave themselves some hope when they scored their second goal in the 88th minute through Theingi Tun while Khin Marlar Tun fired in from range two minutes later but that was to be it for them.
“I thought that Vietnam were under more pressure than us in this match,” said Myanmar head coach Win Thu Moe.
“If the game had been five minutes longer, I thought that we could have drawn the match.”
Earlier, the Philippines had to throw everything they had to hold hosts Indonesia to a 3-3 draw.
Philippines dominated the first half, with Inquig Kyla Jan Aragones firing in an eighth minute free-kick as they then doubled their advantage five minutes later when Semacio Joyce Omboy latched on to a cross from Kathleen Rodriguez.
“Unfortunately we couldn’t score a win today. There were only 30 seconds left and Philippines scored to seal a draw at the end. But I appreciate the effort of the players,” said Indonesia head coach Satia Bagdja.
The half-time pep talk by Satia seemed to have fired the home team as Zahra Muzdalifah headed in a free-kick from Yudith Sada to level the tie.
In the 63d minute, striker Mayang lobbed in a fabulous free-kick from just outside the Philippines box to beat custodian Stavey Cavill for the second time.
All pumped up, Indonesia finally went ahead for the first time in the game in the 82nd minute with Syenida Meryfandina blasting in from a Mayang playback.
But in their haste to pick up their first win of the competition, a late corner allowed Quinley Quezada to outjump her marker and head the ball in for the teams to share points.
“This is the most interesting match we’ve been through so far because we played against the host team in our last match. A little unsatisfied because my players did not do well in the second half,” said Philippines head coach Letecia Callejas.
Indonesia 3 Philippines 3
Vietnam 4 Myanmar 3
Semi-finals (Local time)
Thailand vs Myanmar (16:00)
Vietnam v Australia (16:00)
Sources: aseanfootball.org, Football Association of Indonesia