Ireland succumbed to the Japanese due to a lack of leadership and being affected by the conditions in Shizuoka, according to the Irish Independent's Ruaidhri O'Connor.
Ruaidhri joined Off The Ball for Monday Night Rugby, where he opened up on why things culminated in a 19-12 loss to the host nation on Saturday.
"I never felt like they were in control of the game. From the start of the game, the energy levels were off where they were against Scotland," said O'Connor.
"It brought me back to Cardiff four years ago, when Ireland put all of their eggs into beating France with this emotional, intense performance that resulted in them getting out of the pool. A week later, they couldn't get to that pitch again.
"I felt like they couldn't get to the same emotional pitch a week later against Japan, in a game that as - if not more - dangerous than Scotland."
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O'Connor believes that a lack of leadership was crucial to Ireland's loss, in light of Johnny Sexton's absence.
"It is becoming increasingly apparent that the other leaders on the team look to the chief leader in Johnny Sexton.
"When things were going badly, they needed him to make the decisions because they weren't making the decisions."
Ruaidhri also believes that it was atmosphere - both temperature and among the fans - did for Ireland on Saturday.
"The humidity was much higher in Shizuoka than it was in Yokohama, and I have never experienced a wall of noise like what greeted everything Japan did positively," said O'Connor.
"I didn't think they had a huge amount of control on the pitch, even though they had control on the scoreboard.
"Once the penalties starting going against them, once the line-outs started to melt down, they started making on-the-fly decisions and trying things that they don't normally try.
"They stopped doing the things that they were doing well in the first 20 or 30 minutes. Jack Carty did not try another cross-kick after the one that came off on the edge of the 22 for Keith Earls."
The Japanese fans can take partial credit for Ireland's demise.
"The noise that greeted that scrum penalty after 22/23 minutes - I have been to sporting events of all sorts, and I have never heard anything like it.
"I think it was an assault on the Irish senses. If they were at end of 2018, then I think they would have been able to handle things the way Wales did [against Australia.]
"But because they are at the end of 2019, they started to doubt themselves and their own decisions."
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