Jamie Joseph is not getting carried away with Japan's Rugby World Cup campaign just yet, despite an incredible victory over Ireland on Saturday.

The host nation made it two wins from two in Pool A by upsetting a side that had been ranked the best in the world coming into the tournament, winning 19-12 with a superb fightback.

Japan are now in pole position to top the group, but they must first beat Samoa and Scotland before considering their path deep into the competition.

The Brave Blossoms defeated South Africa in their opening game in England four years ago but lost to Scotland and agonisingly crashed out with three victories.

Joseph is keen to avoid a repeat, telling a news conference: "We could be in a situation where we win tonight and lose to Scotland and miss out - that's certainly what happened last time - so we're certainly not getting ahead of ourselves.

"The boys will have a couple of beers tonight, no doubt, and then we've got Samoa ahead of us."

The coach revealed Japan had been focusing on this match for 12 months and felt that gave them an advantage over Ireland, who have been in Six Nations action in that time.

"Obviously the Irish team is a quality rugby side, but we have been preparing for this game for a hell of a lot longer than the Irish have," he said.

"I said to the players that we've been focusing on today for the last year at least and probably, subconsciously, the last three years. They've only been focusing on it since Monday.

"We felt like we had a bit of an advantage in that and we just needed to execute our plan, which the boys did."

But Joseph also praised Japan's mental fortitude in standing up to the late pressure from Ireland as they chased the game.

"The big focus for us this week was to put two in the tackle as we knew how Ireland would come at us," he said.

"They surprised us a bit with their kicking game, the crosskicks to our wingers, and caught us out a couple of times and scored a try. That was something we had to adjust to.

"But all teams go to a certain pattern under pressure so, when we got ahead, Ireland tried to take us on physically and, I think, mentally we were prepared for that.

"It's easy to say you're mentally prepared but you've still got to make those tackles.

"There were some critical turning points within the game where the players just showed some courage really and were able to hold out a really tough Irish attack. It's those moments in big games of rugby that really turn the game, so I'm proud of our boys."