Vietnam, who are managed by former Japan coach Philippe Troussier (68), took a shock 2-1 lead in their Group D opener before four-time champions Japan roared back to win 4-2.
"Some fans may be unsatisfied with conceding two goals against Vietnam. People may have expected us to win by more goals, but it doesn't make a difference to how we prepare," Moriyasu told reporters ahead of their second game against Iraq.
"Negative news is not a bad thing, it shows people are watching us. I don't really mind criticism.
"It's natural (in football), what we managed to do and couldn't do. I'm not worried about what we couldn't do, but it's important to learn from our mistakes. What we could do we can do better, but we're preparing normally."
Japan defender Ko Itakura (26) echoed his coach's sentiments, saying things do not always go according to plan in big tournaments like the Asian Cup.
"What we experienced was unexpected in the Vietnam game," said the centre back, who plays for Borussia Monchengladbach.
"We didn't take it for granted, but we can take many positive things from the game to play better in upcoming games."
Their next opponents Iraq are one of the West Asian heavyweights who won the tournament in 2007.
Although Japan are unbeaten in their last nine games against Iraq, they have not played each other since 2017 and Moriyasu said he expected a far more physical contest compared to the Vietnam game.
"We've been analysing them for the last few games. They're physically strong, but they can play well together as a unit. That's my impression of the team," Moriyasu said.
The coach also said Arsenal full-back Takehiro Tomiyasu (25) is back in training after missing the first game and is in contention to play against Iraq.
