Japan lost 35-13 to Ireland in the second test of their two-match series at Ajinomoto Stadium on Saturday.

A dress rehearsal for Rugby World Cup 2019, when the stadium hosts the opening game and the two sides have been drawn together in Pool A, the game left many in the crowd of 29,354 confused as to what the real Japan is.

An error-ridden first half was followed by a much-improved second half as the hosts lifted their game and the visitors struggled with the heat at the end of a long season.

"I am very proud of the way we fought to the end," said Japan coach Jamie Joseph. "In parts they overpowered us but no one gave in. We challenged them at the breakdown but our accuracy cost us. And we gave away far too many penalties, which you can't do at test-match level."

Kotaro Matsushima showed what Japan can do when they get ball in hand, Kenki Fukuoka defended well and Luke Thompson performed heroically on his one-off return to international duty, making 24 tackles.

But in the end, Ireland's experience allowed them to hold on for the win.

"Having spoken to the players, that was very tough going," said Ireland coach Joe Schmidt. "Japan were quick off the line, tough at the tackle and made it very hard for us to win the game."

Following last week's 50-22 defeat in Shizuoka, Japan needed to start well.

But once again they learned the hard way that unforced errors get punished by top teams.

The game was just three minutes old when a loose pass in midfield from Amanaki Lelei Mafi was scooped up by Garry Ringrose, who sprinted over for the opening try.

"I talked to Garry after the game and we agreed it was a 14-point try because if he didn't pick it up we had numbers out wide and could have scored," Thompson said.

Josh van der Flier then got his name onto the scoresheet shortly after following a sustained period of pressure as Ireland used their forwards to suck in the Japan defense and create numbers out wide.

Japan tried to fight back with their high-tempo game and a penalty from Jumpei Ogura saw the hosts on the scoreboard in the 14th minute.

But missed tackles allowed Ireland to stretch their lead with Kieran Marmion finishing off a powerful break from Jack Conan in the 17th minute.

Rugby - Japan, Ireland - Ireland fans 

Starved of the ball for long periods it looked like being a long afternoon for the Brave Blossoms.

But they came alive in the 23rd minute, when a superb break from Uwe Helu was finished off by Matsushima in the corner.

With most of the 50-50 decisions from referee JP Doyle and his assistants going the way of the visitors, though, Ireland added a further try through Rhys Ruddock to lead 28-8 at the break.

"It was very hot out there and the players were fatiguing early in the game, so it was great to get a good start," said Schmidt.

Japan's errors continued immediately after the intermission with a knock-on close to the line ruling out a try by Shuhei Matsuhashi.

A score at that stage could have changed the complexion of the game, but with Japan continuing to be penalized -- much to the bewilderment of players and fans alike -- the Irish were able to regroup.

With one decision finally going Japan's way -- after the TMO intervened and ruled an intentional knock-on in favor of the hosts -- Akihito Yamada flew over for Japan's second try in the 62nd minute.

The Brave Blossoms threatened to pull even closer, but errors at the line-out and some stout Irish defense ensured they were unable to get any closer and the game closed out with Sean Reidy crossing for Ireland's fifth try, which like the previous four was converted by Paddy Jackson.

"One of the biggest differences today was simply the mental toughness," said Japan captain Michael Leitch. "Some teams give up after 50 minutes because they get tired but Ireland just kept going."

For the Irish, the game marks the end of the season. For most of the Japan team there are still three Super Rugby games to be played, before they get just five weeks off prior to the Top League kicking off.

"The game today highlights the gap between Tier 1 teams and where we are now and what we are working towards," said Joseph.