Keith Earls, Dan Leavy and Jack Conan ran in two tries apiece and Garry Ringrose also touched down in the victory, with three of those scores coming during Heiichiro Ito's costly sin-binning midway through the first half.
Joe Schmidt's men were ruthlessly efficient as they tore into a 31-3 half-time lead, but Japan showed glimpses of their quality in an improved second half showing which culminated in two late tries from Kenki Fukuoka and Yutaka Nagare. Those concessions will rankle Ireland and ensure that they have plenty of defensive drills in the lead up to next Saturday's rematch in Tokyo.
The first Test at Ecopa Stadium - one of the World Cup venues in two years' time - will live long in the memories of Kieran Treadwell and Rory O'Loughlin who were both sprung from the bench to make their Ireland debuts, making it seven new caps so far on this tour.
Rory and Niall Scannell became the fifth set of brothers to start a Test for Ireland in the modern era, following in the footsteps of the Wallaces (Richard and Paul), the Easterbys, the Bests and the Kearneys. There was also a personal milestone for the in-form Earls who set a new Irish record for the most tries scored in an international season - his nine tries eclipsed Denis Hickie's eight from the 2002/03 campaign.
Paddy Jackson's first start in green since February saw him wield plenty of influence at half-back alongside his former Under-20 team-mate Luke McGrath. Jackson had a 100% return off the tee, nailing five conversions and a penalty for a 13-point haul.
Leavy, Conan and Cian Healy all impressed up front, as did an authoritative Irish scrum, while updates will be awaited on injuries picked up by Simon Zebo (knee), Jackson (shoulder/ribs), Finlay Bealham (blood), and McGrath who, like Earls, was a key figure in some of Ireland's best attacks.