Ireland Flyhalf Jonny Sexton wants his team mates to not dwell too much on their shock loss to Japan. Photo: Rebecca Naden/Reuters

KOBE Ireland made mistakes in every department in their shock 19-12 defeat to Japan and have to figure out why it happened to make sure they still qualify from Pool A, flyhalf Johnny Sexton said on Sunday.

Sexton was not risked on Saturday because of the minor thigh strain he picked up in their opening win over Scotland.

Yet as one of Ireland's two vice captains he gave a frank assessment after diving straight into the video analysis, with an encounter against Russia to come on Thursday.

"It wasn't just one thing. Discipline was obviously a big one that we don't normally do. Any marginal decision we were on the wrong side of and we looked at those penalties today and yeah, they can be penalties so we've got to look at ourselves there," Sexton told a news conference.

"There was a lot of access points we gave them. We had them under pressure a few times and let them out, we didn't exit a couple of times as well as we should have. There was one or two things in each department that added up and they played brilliantly on the day."

Sexton, Ireland's lynchpin in recent years, admitted it was frustrating not to be on the pitch to help out, but that the coaching staff wanted him to sit the game out after not training fully.

"It's very hard to know unless you're on the pitch at the time," Sexton said when asked if his experience would have made a difference in the second half when Ireland failed to score and were thoroughly outplayed by Japan.

"We've got to figure out why it happened. The only blessing in disguise is that the last two World Cups, we've had everything go our way and had the day that we had yesterday in the quarter-finals and we'd be going home today. The great thing now is we've got the rest of the pool to get things together."

Ireland will qualify for the last eight with bonus-point wins over Russia and Samoa, and could still top the pool if Japan fail to win their remaining two games.

They will have to target a big win over the Russians without Chris Farrell, who has a confirmed concussion and will make a decision on fellow centre Robbie Henshaw's fitness over the next couple of days, forwards' coach Simon Easterby said.

"We've responded really well in terms of the other (recent)setbacks, things weren't going our way at the start of the Six Nations, we had a brilliant performance against France. Things went bad against England, we beat Wales back to back and we started with a bang last week against Scotland," Sexton added.

"If we can go on a bit of a run now, a five-game winning run would be great. That would do nicely." 

Reuters