Vietnam finished top of Group K, while Thailand, who already have a place in the Finals, took second spot.
Thailand started the match strongly but it was Vietnam who were more threatening as they opened their account in the 17th minute through Ha Duc Chinh as the young Golden Dragons took a 1-0 lead into half-time.
The War Elephants tried to dominate the match after the restart but Nguyen Hoang Duc struck in the 53rd minute to widen Vietnam's lead.
There was more agony for Thailand as they were left with a man down as Supachai Jaided was sent off four minutes later and that created more opportunities for Vietnam.
The young Golden Dragons bombarded the Thai defence and were rewarded for their persistence with further goals from Nguyen Thanh Chung in the 63rd minute and Tran Thanh Son (90+4) as the 2018 runners-up sealed a comprehensive victory.
Indonesia turned in a solid performance, scoring a goal in each half to finish third in Group K.
The Young Garudas took their time to settle into the game against a Brunei side who were also looking for their first win in the Qualifiers.
Dimas Drajad found the back of the net in the 31st minute to secure the lead for Indra Sjafri’s side as Indonesia imposed themselves in the match with the majority of possession as they took a 1-0 lead at the break.
Sjafri's introduction of Egy Maulana at the hour mark made the difference as the midfielder caused problems for the Brunei defenders.
Indonesia began to increase the intensity of their attacks but Brunei held firm at the back. But it was not long before Brunei cracked under pressure and conceded another goal.
Muhamad Rafi Syarahil found space in the danger area before unleashing a left-footed strike to find the back of the net in the 79th minute.
However, Brunei were thrown a lifeline in the 81st minute when Azreen Eskander was brought down in the box by Indonesia goalkeeper Muhamad Riyandi.
Muhamad went on to save the penalty but picked up a second yellow card for an infringement to receive his marching orders. Drajad took up goalkeeping duties for Indonesia but was unable to stop Azim Izamuddin Suhaimi from scoring the re-take.
With Indonesia one man down, Brunei peppered the goalmouth but Drajad stayed firm as the Young Garudas held on to win 2-1.