The Vietnamese team had a great start when they took the lead after just three minutes through Pape Omar’s goal.
They continued to press forward but seemed to lose concentration and let the home team score twice in the 13th and 26th minutes.
Some of the players on either side could not keep their cool in the sizzling heat in Thuwanna YTC Stadium, Yangon. Four times Yangon United’s Seykou Sylla got his elbows into the faces of Hanoi defenders but only received a yellow card.
Hanoi FC coach Chu Dinh Nghiem successfully persuaded his players to calm down and play slower to recover their rhythm.
In the 33th minute, striker Ganiyu Oseni leveled the scores after a one-two with Do Hung Dung. In extra time in the first half, Oseni completed a brace with a chip over the Yangon goalkeeper.
In the second half the weather got cooler but in the stands Yangon United fans raised the temperature with their raucous cheering.
Hanoi continued to dominate with 65 percent of the possession, but missed several chances to score.
Omar scored from a header in the 81st minute and tapped it in to complete his hattrick two minutes later.
With the 5-2 victory, Hanoi FC have gone to the top of group F with seven points. Singapore’s Tampines Rovers are also on seven points but have a game in hand.
Vietnam's Becamex Binh Duong are also in the tournament. They are now in the second spot in group G with seven points after four games.