Shizuoka - Ireland served Japan a brutal reality check as they crushed the Asian champions 50-22 on Saturday in the second of their three-match summer tour.
Joe Schmidt's second-string side ran in seven tries in a clinical performance despite the lingering effects of jet-lag and blazing heat in Shizuoka, on Japan's Pacific coast.
"The conditions probably helped as both teams came to play good rugby and throw the ball around," said Ireland's stand-in skipper Rhys Ruddock.
"It was really physical and we're feeling it after that."
With the bulk of Ireland's usual starting line-up in New Zealand on duty with the British and Irish Lions, a fresh crop of hungry young players tore into Japan from the start.
Keith Earls burst clear to score Ireland's first try after 10 minutes and, with Heiichiro Ito sin-binned, Dan Leavy barged over twice before Jack Conan also crossed as the tourists stretched their lead to 31-3 at half-time.
The Irish, who arrived in Japan earlier this week after thrashing the United States 55-19 in New Jersey, added further tries through Conan's second, Garry Ringrose and the effervescent Earls again after the interval.
Fly-half Paddy Jackson slotted 13 points on six-for-six kicking.
Japan's "Brave Blossoms," who ground out a 33-21 home win over Romania last week, looked bereft of ideas in a dress rehearsal for the 2019 World Cup, when they face Ireland in the pool stage as tournament hosts.
Ryuji Noguchi finally crossed the try line on the hour-mark and late efforts from Kenki Fukuoka and Yutaka Nagare at least offered crumbs of comfort for Japan, who get another crack at the Irish in Tokyo next week.
"Japan showed in the second half what they're about," said Rudduck.
"After seeing how difficult it was to defend them in the second half we will have to tighten up defensively next game."
Japan have never beaten Ireland and the last time they met before Saturday was in 2005.
Asia's top side have made real progress since, shedding their tag as World Cup pushovers by winning three games at the 2015 edition under former coach Eddie Jones, including a stunning upset of South Africa.
But Japan rarely threatened a much-changed Ireland side, while further ill-discipline is likely to cause concern for head coach Jamie Joseph.
"It's really disappointing," said Japan captain Shota Horie. "We have to tighten up and improve for the next game.
"Ireland are a very physical team, which is also an area we need to compete better in as we build toward the 2019 World Cup."