Many chances were created from the beginning of the match between the two ASEAN arch-rivals but none were converted.
Early in the second half, the tight battle was broken as Quynh nabbed the only goal of the game in the 50th minute, delivering victory to Vietnam who then secured top place of Group A with maximum four wins from four.
Vietnam will take on Myanmar, Group B's second-place team, in the first semi-final, while Thailand will play Group B winners Australia on August 2 at the Gelora Jakabaring Stadium later.
Also on July 30, Singapore and Cambodia played a 1-1 draw to complete their group fixtures at the Jakabaring Athletic Field.
It was Cambodia, who went ahead in the 53rd minute through Von Sreynou before Singapore replied through Nurzaherra Maisarah Rostam in the 79th minute.
