Ireland dominated Japan to claim a 50-22 win in their Test series opener in Shizuoka on Saturday.
A much-changed and inexperienced Ireland had few troubles in Japan, crossing for seven tries in what was the first meeting between the nations in 12 years.
Dan Leavy, Jack Conan and Keith Earls each scored two tries, while Garry Ringrose also went over for the visitors.
Earls' double saw him set a record for most tries in a season for Ireland with nine.
Paddy Jackson finished with 13 points via five conversions and a penalty as Ireland made it six wins in as many matches against Japan.
They led 31-3 at half-time and when Conan crossed again shortly after the break, there was no way back for Japan.
The teams meet again in a second and final Test in Tokyo in a week's time.