Joe Schmidt admits Ireland are now in a World Cup "dogfight" after the stunning 19-12 defeat to Japan.
Bouyed by an opening-match win over Scotland in Pool A, Ireland must now hope for results to go their way in order to avoid a probable quarter-final meeting with New Zealand, who are favourites to top Pool B.
Ireland's next match is on Thursday against Russia.
"I felt we got off to a good start and we controlled the first quarter, mostly, and went up 12-3 after a couple of good tries, the second of which was on the back of two penalty advantages so we were really starting to squeeze them and they were making errors," the head coach told RTÉ Sport.
"I suppose it reversed. We got penalised four times for offsides.
"Watching the monitor they were some pretty tough calls but I think it gave them a bit of oxygen and they didn't need too much, they were superb tonight.
"They got off the line and really put us under pressure and even when we did make a few line breaks they were incredibly quick to get back and put us back under pressure so yeah, look, it’s one of those evenings where if you are not quite up to the mark these guys are going to knock you over and take advantage.
"They take control of the pool now, they’ve got Samoa and Scotland left.
"It will be a real dogfight now through to the end of the pool."
Japan had two extra days to prepare following their victory over Russia and it was something Schmidt pointed to afterwards.
He added: "We didn't do a lot during the week. We had a six-day turnaround, I know it sounds like a broken record: eight-day turnaround versus six-day turnaround, it does make a difference.
"You get a little bit more time to recover and a little bit more time to put a plan together and we knew that was coming.
"I think conditions were pretty tough for us but they are the same for both teams, the humidity, the heat, it is pretty tough going.
"We’ve got to be able to get beyond that. We’ve got another game in five days.
"It’s not like you can start feeling sorry for yourself, you've got to pick yourself up and immeditaly put a plan together to try to make sure we get the result we need against Russia to stay in the race for this pool."