Hamamatsu - World Cup hosts Japan are confident of "beating anyone", livewire scrumhalf Yutaka Nagare said ahead of their crunch Pool A match against Ireland on Saturday.

Four years ago Japan shocked the sport by pulling off a thrilling 34-32 victory over South Africa and it is a measure of just how far the Brave Blossoms have come that their players believe they can push one of the northern hemisphere's best teams.

"We're confident of beating anyone in the world," said a defiant Nagare, who edged out Super Rugby veteran Fumiaki Tanaka for a starting role in Japan's 30-10 victory over Russia in Tokyo on Friday.

"When we reviewed the Russia game, it was actually better than we thought. There was a lot of pressure and we got a little flustered, but we played quite well.

"It's all now about belief in what we've accumulated in training. We need to demonstrate intent and attention to detail."

Nagare added: "This is a World Cup, you always need to give 100 percent to be able to win, as was the case for Russia and will be the case for Ireland.

"My mindset is that we need to beat them to make the last eight."

Joe Schmidt's Ireland, however, will be a different proposition from what was in essence a very limited Russian side that briefly made the most of a very nervy start by Japan under the watchful glare of a home support with large expectations.

The Irish, briefly World Rugby's number one ranked team in the build-up to the World Cup, kicked off their campaign with a comprehensive 27-3 victory over Scotland.

"Ireland don't make many mistakes and they're very resilient, a very strong, quality side who don't panic," acknowledged Nagare.

"We need speed in our game and to maximise space when it comes. We expect them to kick so we also need to utilise the ball they kick our way in a productive manner."

Nagare pinpointed the halfback pairing of Conor Murray and current World Rugby player of the year Johnny Sexton as "key players".

"If we let them play comfortably they'll dominate the game so it's important we put immense pressure on them early on so they feel as uncomfortable as possible!"

The scrumhalf added there had been no need for motivational talks based around that victory over the Springboks four years ago.

"We haven't spoken about past achievements. Everyone thinks Ireland will win. Ireland are expected to win, but we truly believe we can prove them wrong," Nagare insisted.

"We're just focused on beating this team."

There was, however, a bigger picture, Nagare admitted, with the goal of Japan hosting the World Cup to get "rugby promoted and bigger".

"I watched Japan beat South Africa in 2015 and it really inspired me to make the team," said the 26-year-old.

"Hopefully hosting this can help make Japanese rugby better quality."