Ireland have issued a strong endorsement of "laid back" Jack Carty's ability to boss the backline in Saturday's World Cup clash with hosts Japan.

Connacht fly-half Carty only made his international debut in Italy in February, and now the 27-year-old will make his second Test start against the Brave Blossoms.

Ireland had the more experienced Joey Carbery available for selection but head coach Joe Schmidt opted to start Carty instead, following his impressive showing off the bench in the win over Scotland in Yokohama.

Johnny Sexton is being protected after a bang to the thigh, but Ireland remain unfazed by the absence of 2018's World Player of the Year.

British and Irish Lions scrum-half Conor Murray admitted he relishes linking up with Carty, a playmaker he believes is able to keep his head amid Test arena intensity.

"He's quite a calm character, Jack, which is good to have outside you," said Murray.

"Like anyone that comes into the set-up there's a pressure to learn and step up on you and he's responded really well to that.

"He's got to grips with the way we play, the tactics and phase-calls and what's expected of him.

"That laid-back nature has aided him in coming into an environment like this and learning off the likes of Johnny and Joey, who is actually younger than him but has been around the set-up for a while.

"So, yeah, I'm excited to play with Jack. He takes it in his stride, he's played really well any time he's been given the chance whether in the Six Nations or the summer series, coming over here and coming on last weekend he did really well. I'm excited."

For Carty, the span from uncapped rookie in February to trusted World Cup starter in September is some jump. But defence coach Andy Farrell believes he has proved himself more than ready for this chance.

Former England coach Farrell hailed Carty for his ability to stay true to his personality amid the obvious demands of fitting into boss Schmidt's demanding team structure.

"International rugby is a pressure occasion for anyone, especially when you're coming into a side when you're new to the environment and you've heard from the outside what it's like," said Farrell.

"All of a sudden you're in the mix and you either sink or swim, don't you, with all the information you've been given that everyone is unbelievably comfortable with.

"And I think Jack's strength of character is one of not just his work ethic to get across his detail, but also being himself.

"That's the most important thing. You want to see guys who are in pivotal positions being able to retain the information but also see the game as it is unfolding and he's comfortable with doing that."