Ireland coach Andy Farrell wanted a convincing show at home after losing to New Zealand 26-13 in Chicago and Japan looked to be there for the plucking on Saturday after being smashed by South Africa 61-7 last weekend.
The hosts' first 10 points all came from flyhalf Jack Crowley, a penalty, try and conversion - the latter pair shortly after a yellow card for Japan centre Charlie Lawrence blunted the visitors' encouraging start.
Ireland welcomed back captain Caelan Doris but it was one of the handful of fringe players given a chance - flanker Nick Timoney - who added a second try.
Eddie Jones' Brave Blossoms trailed only 17-10 at half-time following Kenji Sato's score and five points from the boot of Lee Seung-sin.
But while winger Jacob Stockdale was sent to the sin bin at the end of the half, Ireland were far better in the second period.
And further tries from Andrew Porter, replacements Gus McCarthy and Paddy McCarthy, plus wing Tommy O'Brien, eventually saw Japan overwhelmed.
"We wanted to put in a better performance for the home crowd," Ireland standout O'Brien told broadcaster TNT.
"We brought plenty of energy and improved massively in the second half. We had a few new players out there today and tried to play a fast brand of rugby so that will come with errors."
