Iran, looking to end a 43-year title drought since last winning Asian football's most coveted prize, could have scored four or five but for some poor finishing in Abu Dhabi.
"But winning is the best medicine in football. To win two games and score seven goals -- I have to praise my players because I am very demanding."
Saman Ghoddos and Mehdi Taremi went close for Asia's top-ranked team before Azmoun rose to head home a Ghoddos cross after 38 minutes.
"We just need to relax more," said Queiroz. "In the second half our anxiety to score a third goal led to some bad passes.
"He's a finisher," said the Portuguese, now in his eighth year as Iran coach.
"We have high hopes for him for this competition. But the way the team is contributing around him, and our movement in the last third, are very interesting."
While Queiroz comes into the Asian Cup after almost steering Iran to the World Cup knockout stage last year, Vietnam coach Park Hang-seo lamented the gulf in class between Team Melli and his Golden Dragons.
"Iran are ranked 29th in the world, we're 100th," shrugged the South Korean, whose team suffered a last-minute 3-2 defeat by Iraq in their opening game.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)