Captain Michael Leitch has revealed the practice secret that helped Japan handle Ireland’s powerful scrum during their shock Rugby World Cup victory over the Pool A favourites.

“For one week we were constantly focusing on putting together our best scrum,” Leitch told reporters on Sunday.

“The same way we prepared for the (pre-World Cup) South Africa match, we did 8-on-10 scrums to practise holding up against the opponent’s pressure.

“I think the players’ scrum (against Ireland) was their best ever.”

The Brave Blossoms were less successful against the Springboks, wilting 41-7 in their World Cup warm up match earlier this month.

But the hosts turned it on when it counted, stunning world No.2 Ireland 19-12 on Saturday to record their second win from two matches in the tournament and put themselves in prime position to advance to the quarter-finals for the first time.

Japan won all six of their scrums. And during an Irish attacking scrum just before halftime – in what turned out to be a key momentum changer – the lighter Japanese pack drove back the Irish front eight before winning a penalty.

Ahead of the match, Ireland scrum coach Greg Feek had flagged the Japanese scrum as one of the big challenges they would face.

The Japanese next take on Samoa on October 5, and Leitch said matching the Samoans’ physicality would be crucial.

Mindful of their pool-stage exit in England four years ago despite winning three matches, the hosts are taking nothing for granted despite their perfect 2-0 start.

“Samoa will be a really important game for us. The Samoa players are of course strong and in the last tournament were very physical. So I think defence and pressuring them will important,” Leitch said.

“We’re not looking ahead to the Scotland match. We have to take it one game it a time.”

Japan’s historic win against the Irish means rugby fever has reached new heights across the country but Leitch said the players would need to stay grounded and avoid the distractions.

“It’s important our preparation doesn’t change,” said Leitch. “With all this attention we’ll get emails from friends and fans and various people and have to be prepared for that.

Just yesterday I got about 200 Line messages and can’t respond to everyone. I’ll answer them after the tournament’s over.”