Conor Murray will make his full Test debut when Ireland open their World Cup campaign against the USA on Sunday.
Murray, who at 22 is the youngest member of the squad, won his two caps as a second-half substitute against France and England last month.
It is a bold selection by coach Declan Kidney given that Murray only broke into Munster's first team this year and has yet to play in the Heineken Cup.
But he did enough in the warm-up Tests and during his time in camp this summer to secure a place alongside Jonathan Sexton at half-back, with Eoin Reddan dropping to the bench.
"Conor's been going well in training and we said we'd judge it off that. If we're to know more about him, now's the time to know," said Kidney.
"He deserves a go and we think he's good enough to start. It's a big call given it's our first game in the World Cup, but what he's been doing merits his inclusion."
Flanker Sean O'Brien and full-back Rob Kearney have been omitted from the 22 as a precaution.
The Leinster duo have been passed fit from their respective knee and groin injuries but Kidney, mindful of the clash with Australia next Saturday, has given them another week to recuperate.
Ireland team: Geordan Murphy; Tommy Bowe, Brian O'Driscoll, Gordon D'Arcy, Keith Earls; Jonathan Sexton, Conor Murray; Tom Court, Rory Best, M Ross, Donnacha O'Callaghan, Paul O'Connell, Stephen Ferris, Shane Jennings, Jamie Heaslip.
Replacements: Jerry Flannery, Tony Buckley, Donnacha Ryan, Denis Leamy, Eoin Reddan, Ronan O'Gara, Andrew Trimble.