As expected, Jordan Larmour and Andrew Conway will deputize at fullback and wing. Coach Joe Schmidt had no doubt the pair, appearing in their first World Cup, will compensate for the loss of a pair at their third World Cup.
"Their enthusiasm is something that's contagious, their ability to get themselves into the game," Schmidt said of Larmour and Conway. "They're feeding off each other, and they are very, very keen to impress. Now they have that opportunity."
Center Robbie Henshaw was already ruled out with a hamstring that tightened in training last weekend, and flyhalf Joey Carbery was still recovering from an ankle injury against Italy six weeks ago. All four backs are expected to be available to play Japan in eight days.
With Henshaw out, Garry Ringrose was partnered with Bundee Aki in midfield. From the pack which overwhelmed Wales in Dublin two weeks ago, lock Iain Henderson was in for newcomer Jean Kleyn, and Peter O'Mahony was back on the blindside flank, bumping CJ Stander to his usual No. 8 spot.
Only Henderson, front-rowers Cian Healy and captain Rory Best, and scrumhalf Conor Murray were in the match-day 23 against Argentina four years ago, when Ireland lost in the quarterfinals. That result prompted Schmidt to strengthen the squad to ensure they wouldn't be caught short by injuries again. He admits he's nervous to see four years of planning come to fruition.
"You never quite know," he said. "But one thing I'll be really confident of is that we'll be tough to beat. "In 48 hours' time you'll see a very collective effort, and that effort will make us tough to beat. I've no doubt that the Scots will have been working away and will make themselves something similar.
"I don't think there's a huge amount between the two teams, so whoever does get the bounce of the ball or just be a little more efficient than the other just may tip the balance."
Ireland: Jordan Larmour, Andrew Conway, Garry Ringrose, Bundee Aki, Jacob Stockdale, Jonathan Sexton, Conor Murray; CJ Stander, Josh van der Flier, Peter O'Mahony, James Ryan, Iain Henderson, Tadhg Furlong, Rory Best (captain), Cian Healy. Reserves: Niall Scannell, Dave Kilcoyne, Andrew Porter, Tadhg Beirne, Jack Conan, Luke McGrath, Jack Carty, Chris Farrell.
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