After pulling off the biggest upset of the Rugby World Cup so far by defeating Ireland, Japan still have work to do toward their goal of advancing from the pool stage for the first time, captain Michael Leitch warned Sunday.

"Of course, on the inside I'm ecstatic," the New Zealand-born backrower said when asked at a press conference about the Brave Blossoms' low-key celebration following their historic 19-12 victory at Shizuoka Stadium Ecopa the previous day.

"But it's very important that we now turn to the Samoa game. If we lose our next two games, then yesterday's win will have been for nothing. We've got to keep a cool head and prepare for the next one and then go from there."

Felling Ireland, ranked second in the world going into the match against Japan's ninth, moved Jamie Joseph's men to the top of Pool A with nine points after grabbing a bonus point while beating Russia in the tournament opener.

Japan are now ranked eighth, their highest position ever, while Ireland have fallen to fourth.

If Japan defeats both Samoa next Saturday and Scotland on Oct. 13, that will secure their place in the quarterfinals and have the added bonus of allowing them to avoid an early clash against tournament-favorites New Zealand.

"We need to work on confirming our roles, working out the details, and making sure we have the resolve going into the next game," Leitch said.

"The game against Samoa is very important, and obviously they are a very good side. We played them in the previous World Cup and know they play a physical game. The result is riding on how much pressure our defense can keep on them."

"We're not even thinking about Scotland right now. We need to take this one game at a time."

While the Toshiba Brave Lupus linchpin is focused on the battle to come, he allowed himself a moment to reflect on the previous day's achievement.

"It was the mentality that we want to win, and that we can win, that led us to this victory. We were able to apply pressure in the scrum, the set-pieces, and the maul. Every man did their job."

And of the thunderous home crowd that watched Japan make history again after upsetting South Africa four years ago, he said, "I've played at a lot of stadiums including when we won in Brighton, but yesterday in Ecopa was the best crowd of my life."

"Seeing all the red and white jerseys, and all of the Ireland supporters as well. When we were applying pressure, the cheering was so loud. I think it had an effect on the Ireland players."

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