A headed goal and a penalty from striker Yuya Osako in the second half crushed the spirit of the physical Iranians before Genki Haraguchi made it 3-0 in stoppage time to send the Samurai Blue, who is best known for their technical skills, into a fifth continental title-decider.
"Iran have had great results in the past and we knew they were going to be a very tough opponent, but the players had prepared well and they showed great fighting spirit," Moriyasu told reporters.
"They didn’t forget to have the mindset of challengers and that gave us the win today. The atmosphere was like an away game for us but there were many Japanese supporters and many people back home supporting us too.
"I’m happy the players could show the spirit to fight and to deliver a good result."
The Japanese had hardly set the tournament on fire with their previous performances in the United Arab Emirates, winning their three group games by the margin of a single goal and knockout matches against Saudi Arabia and Vietnam 1-0.
"I don’t think we changed compared to how we have played in the previous matches, but what our players did today was ... try to perform to their best individually and as a team and play for the result," Moriyasu added.
"Knowing that Iran have a strong attack and are strong physically, the players were aggressive and showed a lot of fighting spirit, and that was the difference. They tried to win the second ball and they were persistent."
Japan have won all four of their previous Asian Cup finals and will go into Friday’s showpiece against the UAE or Qatar at Zayed Sports City as favourites.
The former Japan under-23 coach said they would maintain their pragmatic approach against whoever got through Tuesday’s second semi-final in Abu Dhabi.
"There wasn’t just one style of play in this match, but the players showed flexibility and that’s what got us the result," he said.
"In the final we will have our football ideals, but when we face the reality we will adjust to that."