Three wins by a single goal margin in the group stage were followed by a 1-0 victory over Saudi Arabia in the last 16 and a VAR-assisted triumph over Vietnam by the same score in Thursday's quarter-final.
Moriyasu raised hopes of the Samurai Blue embracing a more attacking style when he took over after last year's World Cup, with his young side scoring 15 goals in winning four of five matches and drawing the other at the Kirin Cup tournament.
That optimism has dissipated in the United Arab Emirates, with a safety-first policy dictating Moriyasu's tactics as Japan seek a record fifth continental crown.
"It was good that the players did not concede any goals to Vietnam," he said after the win in Dubai.
"We have had to defend, as was the case against Saudi Arabia, and sometimes we dominated, but couldn't find a way through. These experiences will be used to prepare the team for the semi-final."
Iran have scored 12 goals and conceded none on their way to the last four and are likely to present by far the toughest opposition the Japanese have met in the UAE.
Moriyasu has been keen to emphasise the inexperience of his young squad throughout the tournament and believes they are gradually improving as they play more matches.
"As we have players with little international experience, it is important that they are exposed to tough matches on a big stage like the Asian Cup," he said.
"Playing tough matches and winning in the knockout stage boosts confidence and also leads to the development of the players and team."
(Reporting by Nick Mulvenney, editing by Andrew Cawthorne)
