Vietnam suffered a 1-2 defeat to Iran at the Under-19 Southeast Asian Open contest at Ho Chi Minh City's Thong Nhat Stadium on Sunday.
Facing the powerful rivals, Coach Mai Duc Chung had his footballers assume in a 4-4-1-1 formation but the defensive strategy did not prove effective enough.
The hosts conceded their first goal after Azmoun fired a power shot during their fast attack in the opening minute of the match.
The Vietnamese players tried and failed to rally against the Iranian team, which had taken complete control of the game and doubled the scored 15 minutes before half time.
The host squad improved with the addition of Thai Sung, a young player who recently finished a three-year training course at Qatar's Aspire Sports Academy.
The Vietnamese players' renewed efforts pulled one goal back after Dinh Thang looped the ball over Iran's goalkeeper Sedhi right before the break.
In the second half, the Iranian U19s played slow football but their hosts didn't permit any more scoring chances except during the 80th minute when striker Xuan Nam had only goalie Sedhi to beat but he failed to score the leveler for Vietnam.
In the earlier match, the U19s from Uzbekistan beat Australian U19s 2-1.
The tournament will end on Saturday.