Ireland head coach Joe Schmidt dismissed suggestions his players can take it easy after starting their Rugby World Cup campaign with a resounding win over Scotland on Sunday, warning that "dangerous" next opponent Japan will punish any complacency from the world's No. 1-ranked side.

Ireland began its Rugby World Cup campaign in dominating fashion at International Stadium Yokohama with a 27-3 win over the Scots, steamrolling them with three first-half tries from its forward pack before winger Andrew Conway secured a bonus point with a fourth score.

The result puts group favorite Ireland on a potential quarterfinal collision course with South Africa after the Springboks lost to New Zealand on Saturday night, but Schmidt is not looking that far ahead with Japan next up for his side in Shizuoka on Sept. 28.

"We may be able to manage the squad, you might think, but I know that watching Japan, that first half they played against England, they went through the Pacific Nations Cup unbeaten — they are a dangerous team," Schmidt said of the Brave Blossoms, who began their World Cup campaign with a 30-10 win over Russia on Friday night at Tokyo Stadium.

"If they get some tempo, then we might be on the back foot. We've just got to go step by step. We won't be talking too much about South Africa. If we can maybe get past Japan, we've got Russia, Samoa, and hopefully at that stage we can potentially manage players."

Ireland has two days fewer than Japan to prepare for the match at Shizuoka Stadium Ecopa, and Schmidt said he would have to see what condition his players are in before he picks his team, after a bruising encounter against Scotland.

"It all depends on how the players are," said the New Zealander. "On Tuesday, we may just do a light session, because it was pretty tough out there. I think the Japanese will play very fast. I think they have some great skills. They have players who can spread the ball very quickly, from (Yutaka) Nagare to Yu Tamura.

"Timothy Lafaele is one of the most skillful guys you'll find in a midfield. And on the edges, I thought (Lomano) Lemeki was an absolute wrecking ball against Russia. Up front you've got some really dynamic guys. I'm not sure how (Japan head coach) Jamie (Joseph) will manage those, but we'll be watching with interest on Thursday when he names his team. That might cause a bit of adjustment from us, so that we can best face up to what will be a really tough test for us."

Ireland came into the tournament with criticism ringing in its ears despite being ranked No. 1 in the world, after a series of below-par performances this year.

Schmidt's men finished third in the Six Nations and lost 57-15 to England in a World Cup warmup at Twickenham in August, but they were back to their rampant best when it mattered against a heavily outgunned Scotland.

"You can't really avoid what people say leading up to the game," said winger Conway. "You're definitely aware of it but I actually like that, to be honest. Whenever there's panic, media-wise, about a few lads, it gives you a nice gesture to people who don't think you're up to the task.

"As a team, we're definitely happy with the score line. Scotland probably didn't play as well as they wanted and I'm sure they'll be disappointed with their performance, because they're a really good team. But for an opening game of the World Cup, against a really good Scottish team who we've had trouble with in the past, we're quite happy."

Scotland now travels to Kobe to face Samoa on Sept. 30, with games against Russia and a potential quarterfinal-berth decider against Japan still to come in Pool A.

The Scots have only missed out on the knockout stage once in eight previous Rugby World Cup appearances, but one more defeat in this year's tournament could spell the end for their chances.

"We've got to win every game, but we were going out to win every game anyway," said No. 8 Ryan Wilson. "We were playing a bloody good team in Ireland, and they showed that tonight. They played the conditions well and they controlled the game quite well, whereas we didn't.

"We've got nothing to worry about. We'll bounce back, we've just got to make sure we stay positive. We've got a big test against Samoa, but that's a team that we feel we can play our brand of rugby against and come out on top."

Sunday's game was watched by a crowd of 63,731, with swaths of green-clad Ireland fans at Yokohama International Stadium maintaining a steady vocal support despite a second-half downpour.

"It was crazy," said second-row forward James Ryan, who scored his team's first try. "The atmosphere today, it had a different feel to a Six Nations game or anything I've played in. It was hot."