Pieter Labuschagne will captain Japan when they take on Ireland at Shizuoka Stadium Ecopa in Pool A of the Rugby World Cup with Michael Leitch starting the game on the bench, coach Jamie Joseph said Thursday.

With Amanaki Lelei Mafi fit again, Joseph has opted to move in-form Kazuki Himeno from No. 8 to blindside flanker to accommodate Japan's main strike runner with Leitch dropping to the bench and "Lappies" Labuschagne keeping the No. 7 jersey.

(Pieter Labuschagne of Japan scores his team's third try during the Rugby World Cup 2019 Group A game between Japan and Russia at the Tokyo Stadium on September 20, 2019 in Chofu, Tokyo, Japan.)[Getty/Kyodo]

"What I believe around the game, in terms of our bench, we've got to have an impact," Joseph said of his decision. "If we're going to be in a position to win the match it's going to come down to the last five or 10 minutes, and we'll need clear leadership."

Joseph said Leitch's injury-plagued year had not been a factor, stressing how well Himeno and Labuschagne had played in the opening night 30-10 win over Russia.

"We have a lot of quality loose-forwards and in-form players. So we have in-form players playing really well, and experienced players coming on. So as a coach I get to have both things," he said.

(Jamie Joseph)

Elsewhere in the pack, Koo Ji Won comes in at tighthead prop and Luke Thompson starts at lock as Joseph looks to contain the exact same Ireland pack that destroyed Scotland in their opening game.

In the backs, Ryohei Yamanaka starts at fullback with Will Tupou moving to the wing, in a bid to improve Japan's ability to deal with the high ball.

Swapping a starting role for one off the bench along with Leitch are Asaeli Ai Valu, Wimpie van der Walt and Lomano Lava Lemeki with Hendrik Tui dropping out of the matchday 23.

(Amanaki Lelei Mafi of Japan runs the ball past Ben Volavola of Fiji during the Pacific Nations Cup match between Japan and Fiji at Kamaishi Unosumai Memorial Stadium on July 27, 2019 in Kamaishi, Iwate, Japan.)[Getty/Kyodo]

(Kazuki Himeno)

Earlier, Ireland coach Joe Schmidt named a side showing four changes to the one that started the 27-3 defeat of Scotland last Sunday.

Jack Carty replaces the injured Johnny Sexton at flyhalf, there are recalls for the experienced Keith Earls on the wing and Rob Kearney at fullback while Chris Farrell comes in at inside center.

Schmidt had also hoped to play Jack Conan but the flanker was injured in training so Peter O'Mahony will once again wear the No. 6 jersey despite taking a knock to the head last week.

(Joe Schmidt)

"We always knew we were going to have to manage this start of the tournament because of a six and a five-day turnaround," Schmidt said of his selections.

"So whether guys play this week or next week, we do know that the challenge this weekend will be particularly tough but we also know that we've got to show confidence in the squad, we have that confidence."

Losing Sexton was not, Joseph said, a big blow to the men in green given the depth of their squad. And besides, he added, Japan were focusing more on what they need to do rather than what the Irish will bring to the game.

"I don't think we're the sort of team that can afford to be worried about whether Johnny Sexton is playing or not," he said.

"You don't get to be No. 1 in the world with one or two quality players. While that is a surprise it doesn't change anything that we need to do."

Thompson was the team leader in tackles the last time the teams met back in 2017 and the veteran said "defense would be key" on Saturday as Japan look to keep alive their hopes of top-eight finish.

"They are very organized and good at keeping the ball," he said. "When we have it we need to be patient and keep it. We also need to stick to our systems and be disciplined."