Jack Carty has the full backing of Joe Schmidt to impress at fly-half when Ireland face Rugby World Cup hosts Japan on Saturday.

The top-ranked nation will rest World Rugby player of the year Johnny Sexton after he came off as a precautionary measure in Ireland's first game of the tournament – a 27-3 victory over Scotland – having received treatment on a thigh injury.

Schmidt's side, for whom Rory Best will make a 100th Test start, will face a fervent atmosphere in Shizuoka as Japan look to spring a shock and build on their opening Pool A win over Russia.

But the coach is confident Carty, who has just eight caps, will be able rise to the challenge.

Joe Schmidt has named a strong @IrishRugby team for Saturday’s Pool A match against hosts Japan in Shizuoka.@JackCarty10 starts at 10. While @KearneyRob and @KEITHEARLS87 get their first starts of #RWC2019 #JPNvIRE pic.twitter.com/IL7hDMzDpy
— Rugby World Cup (@rugbyworldcup) September 26, 2019

"We want to give Jack as much certainty as possible, so we told him on Tuesday that he'd be starting and he could get his head around it," said Schmidt.

"He came on and played really well against Scotland, he put in a nice through-ball for Chris Farrell to run on to when he was really under pressure, cleared our lines really well a couple of times when we had to come out of our own '22. The distance and angle of the kicks were spot on.

"He's trained really well, so that gives us confidence and allows us to freshen guys up and work through a few combinations as we work our way through the pool."

Despite Schmidt's praise for Carty, Sexton's absence will provide a boost for Japan, whose coach Jamie Joseph cited the 34-year-old's replacement as someone to target.

"There's a lot less experience without him," the Brave Blossoms boss said of Sexton missing out.

"Johnny Sexton is a key player, but I remember playing my first Test match; it's going to be an exciting time and [Carty's] going to go out and play very well, I believe, unless we can put him under pressure."

History weighs heavily in Ireland's favour, with seven wins from as many matches against Japan, who have lost those games by an average margin of 31 points.

PLAYERS TO WATCH

Japan - Pieter Labuschagne

With regular captain Michael Leitch surprisingly named on the bench for this weekend's clash, Labuschagne will skipper the hosts. The 30-year-old scored a try against Russia and made 18 tackles in a solid display in Tokyo.

Ireland - Jack Carty

When both coaches are talking about one player, it is clear he has to be closely watched. Stepping into the void left by Sexton is a tough enough task in any circumstance, but to do it on this stage represents a true test of character.

KEY OPTA FACTS

- This will be the third meeting between Ireland and Japan at the Rugby World Cup, Ireland beating the Brave Blossoms 32-16 in Dublin in 1991 before securing a 50-28 victory in South Africa four years later.
- Ireland have won their last nine pool stage games in a row at the Rugby World Cup, having never won more than four such games in a row prior to that.
- Two of Ireland's last three pool-stage defeats at the Rugby World Cup have come against the host nation, losing to Australia at this stage in 2003 before a defeat to France four years later (also lost to Argentina in 2007).
- Japan have won four of their five matches at the Rugby World Cup since the beginning of 2015, this after winning just one of their initial 24 matches at the tournament (D2, L21).