Jack Carty will make just his second Test start when Ireland face hosts Japan in Saturday's World Cup clash in Shizuoka.
The Connacht fly-half will pilot Ireland's backline with boss Joe Schmidt not willing to risk Johnny Sexton, who has nursed a minor thigh issue.
Joey Carbery is fit again after ankle ligament trouble and takes a seat on the bench.
Jack Conan was due to start in the back-row but picked up an injury in training on Thursday, meaning Peter O'Mahony was pressed back into service at flanker.
Munster star O'Mahony failed a Head Injury Assessment (HIA) in Saturday's win over Scotland, but quickly passed all the required checks and returned to full training on Tuesday.
Carty impressed off the bench in the closing stages of Ireland's 27-3 win over Scotland in Yokohama, and now the eight-cap playmaker has the chance to impose his presence on this World Cup.
Sexton ceded goal-kicking duties to Conor Murray early in Ireland's win over the Scots, and was withdrawn straight after his side's bonus-point try.
The Leinster star did not train fully on Tuesday, and Schmidt has now chosen not to take any chances with the 2018 World Player of the Year.
Rob Kearney and Keith Earls return to the starting XV having missed the Pool A opener against Scotland due to injury, with Ireland making four changes to their starting line-up.
Kearney has shaken off his calf complaint and Earls is now over his own thigh concern.
While Bundee Aki also completed all the head injury checks and returned to full training, head coach Schmidt opted not to risk Connacht's battering ram centre.
So Chris Farrell starts at inside centre, with the Munster man in fine form and fettle in Japan.
Schmidt has therefore ended up fielding the same pack that subdued the Scots, with Rory Best as captain flanked in the front-row by Cian Healy and Tadhg Furlong.
James Ryan and Iain Henderson will continue their lock partnership that went so well in Yokohama as Ireland flexed considerable set-piece muscle against Gregor Townsend's Scotland.
Ireland boss Schmidt admitted Conan suffered a minor foot problem in training on Thursday.
"With Jack, someone just stood on his foot," said Schmidt.
"He is absolutely fine. But it meant that he was sore in training and he didn't train fully.
"Pete (O'Mahony) is fully fit, Rhys (Ruddock) is fully fit.
"Again it's a case of being confident in the squad, and offering an opportunity.
"And I'm pretty sure Jack will be fine to train tomorrow, but again we rolled our sleeves up today and worked pretty hard so we wanted to get that team to have the chance to play."
— Rugby World Cup (@rugbyworldcup) September 26, 2019
Ireland team to play Japan
Forwards: 1 Cian Healy (Leinster), 2 Rory Best (CAPTAIN, Ulster), 3 Tadhg Furlong (Leinster), 4 Iain Henderson (Ulster), 5 James Ryan (Leinster), 6 Peter O’Mahony (Munster), 7 Josh van der Flier (Leinster), 8 CJ Stander (Munster)
Backs: 9 Conor Murray (Munster), 10 Jack Carty (Connacht), 11 Jacob Stockdale (Ulster), 12 Chris Farrell (Munster), 13 Garry Ringrose (Leinster), 14 Keith Earls (Munster), 15 Rob Kearney (Leinster)
Replacements: 16 Sean Cronin (Leinster), 17 Dave Kilcoyne (Munster), 18 Andrew Porter (Leinster), 19 Tadhg Beirne (Munster), 20 Rhys Ruddock (Leinster), 21 Luke McGrath (Leinster), 22 Joey Carbery (Munster), 23 Jordan Larmour (Leinster)