Ireland are not so far removed from the Six Nations humblings against England and Wales, and the Twickenham debacle, that they can afford to relax.
Sure, the side were outstanding against Scotland, who were terrible, and looked close to their hale and hearty 2018 selves, but the trajectory, which began to rise in the warm-up matches against Wales, must be maintained.
Joe Schmidt's men need to use this match as a springboard into the two lower-profile games (Russia and Samoa) that precede the quarter-final, likely to be against South Africa on 20 October.
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That means that not only must Ireland win the game but they also need to do it with enough style to provide a bonus point and a healthy margin of around 20 points, something which they have achieved in their last six meetings with Japan, including two wins on a summer tour in 2017.
That’s not to suggest that setting such goals means that the game will be won easily – it won’t.
Expect a fit and lively Japanese side, buoyed by the majority of 52,000 crowd in the Shizuoka Stadium Ecopa, to come out swinging.
Talk about coach Jamie Joseph targeting the Scots for a second-place spot may be all the rage but that tie is in the final round, and the Brave Blossoms will have had eight days after their third game to get ready.
Taking the scalp of a team like Ireland would provide an massive boost for rugby in the country.
To get this rare chance and not take a swing at the side that came into the tournament ranked number one would be a missed opportunity.
"If you were in their camp you might even be thinking, 'If we beat Ireland there is no reason that we can’t go and top the group’ and if they were able to do that in a home World Cup that would be incredible," Jordi Murphy told RTÉ Sport.
"They’ve made history before and I’m sure they’ll want to do it again."
The history he refers to is Japan's famous win over South Africa at RWC 2015, when they went on to become the first team not to qualify from a pool with three victories.
Ireland have been warned.
The noise coming the hosts’ camp about the Irish scrum in the build-up to the game seems to suggest that they are worried about that area. Although their starting-pack weight is just 4kgs lighter than Ireland’s, they must know that it’s not a realistic target.
"If you look at Ireland’s scrum over the last two years it’s been very disciplined," Mike Ross told RTÉ Sport during the week.
"From what I've seen a lot of the Japan game plan involves keeping the ball alive and trying to run lads off their feet and they certainly have the personnel to do that.
"They wouldn’t want to get into an arm-wrestle. They’d be more interested in keeping it looser and making Ireland run."
FOOTBALL AND SOCCER'S LOSS WAS IRISH RUGBY'S GAIN AS TALENTED CARTY GETS NOD
Japan, apparently, have been practicing longer training games where the ball-in-play time has been increased from just over 40 minutes to just over 50 minutes.
The theory is that keeping the ball in play in the heat (28c) and humidity (68%) of Shizuoka will test Schmidt’s men more.
"Given what I saw of Ireland’s conditioning at the weekend I don’t think that’s going to be a problem," added Ross.
Schmidt has ended up with the same starting pack that destroyed Scotland, albeit Jack Conan was due to start before a foot injury scuppered his chances.
Greg Feek this morning said that the injury is "a little bit of a setback" but Murphy, who is on standby, is due to start for Ulster against Ospreys tonight. Should he be withdrawn it might be instructive to Conan’s plight.
There was a case to rest captain Rory Best but the Ulster hooker is set for his 100th international start.
"Japan are a better team than they looked against Russia," said Donal Lenihan, the former Ireland captain, of the hosts' 30-10 win in the opening game, in which they struggled to find their feet and looked uncomfortably under the high ball.
Joseph has opted to leave captain and number 8 Michael Leitch on the bench but in comes Amanaki Mafi, the Tonga-born forward who featured in all of their 2015 games and scored two tries.
In the backs, Kotaro Matsushima, who scored a hat-trick against Russia, is the one to watch but the return of Rob Kearney and Keith Earls, who bring 170 caps to the table between them, should have an edge.
The big news from the team announcement was the inclusion of Jack Carty ahead of Joey Carbery, with Johnny Sexton rested with some classification of leg injury.
The call is a huge show of confidence by Schmidt in the 27-year-old, who played his first Ireland game in February of this year and has only started one Test since, the Wales warm-up in Cardiff.
That he goes into Saturday's contest surrounded by what is almost a full-strength side is a great help but if the out-half were to feel nervous it would only be natural.
Ireland are in a good place and this is a good fixture to keep the momentum going.
Verdict: Ireland
Ireland: Rob Kearney; Keith Earls, Garry Ringrose, Chris Farrell, Jacob Stockdale; Jack Carty, Conor Murray; Cian Healy, Rory Best (capt), Tadgh Furlong; Iain Henderson, James Ryan; Peter O'Mahony, Josh van der Flier, CJ Stander.
Replacements: Sean Cronin, Dave Kilcoyne, Andrew Porter, Tadhg Beirne, Rhys Ruddock, Luke McGrath, Joey Carbery, Jordan Larmour.
Japan: Ryohei Yamanaka; Kotaro Matsushima, Timothy Lafaele, Ryoto Nakamura, Will Tupou; Yu Tamura, Yutaka Nagare; Keita Inagaki, Shota Horie, Jiwon Koo; Luke Thompson, James Moore; Kazuki Himeno, Pieter Labuschagne (capt), Amanaki Lelei Mafi.
Replacements: Atsushi Sakate, Isileli Nakajima, Asaeli Ai Valu, Wimpie van der Walt, Michael Leitch, Fumiaki Tanaka, Rikiya Matsuda, Lomano Lemeki.
Referee: Angus Gardner
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