O'Gara, the man of the match against Russia, retains the fly-half jersey ahead of Jonathan Sexton, while Murray gets the nod ahead of Eoin Reddan.
However coach Declan Kidney has denied that O'Gara has been picked for his superior goalkicking at the World Cup.
"Ronan and Conor went well in the last 20 minutes against Australia. Ronan went well against Russia as well," said Kidney.
"This is the right combination for us against Italy. They've played a few times together now.
"Ronan has been place kicking well, but if Jonathan Sexton was starting on Sunday it wouldn't worry me.
"I'd hate to go down the road that we're picking Ronan because of his place kicking.
"He's too good a player to be saying that about him while Jonny's place kicking is not of concern to me."
Ireland need to win the match to guarantee their place in the last eight, with Kidney opting to restore his strongest XV for the encounter.
That means Tommy Bowe and Paul O'Connell have recovered from injuries to return, while Brian O'Driscoll is back to lead the side.
And although Ireland caused a shock in beating Australia earlier in the pool, Kidney knows that win will count for nothing if they slip up against the Azzurri.
"Everyone was talking about the Australia game coming into the World Cup, but in our minds we always knew Italy was the big one," he said.
"Australia was the attractive one to win, Italy was the necessary one to win.
"The law of averages said Australia would beat Italy in the first match.
"Unless you do a New Zealand and get 15 points from your first three games, it was always going to come down to this.
"England and South Africa find themselves in the same situation - three wins from three - yet are also in cup final situations.
"If we were to go out at this stage, well that's life. The Australia win gave us momentum and that was carried on against Russia."
Ireland: 15 Rob Kearney, 14 Tommy Bowe, 13 Brian O'Driscoll (capt), 12 Gordon D'Arcy, 11 Keith Earls, 10 Ronan O'Gara, 9 Conor Murray, 8 Jamie Heaslip, 7 Sean O'Brien, 6 Stephen Ferris, 5 Paul O'Connell, 4 Donncha O'Callaghan, 3 Mike Ross, 2 Rory Best, 1 Cian Healy. Replacements: 16 Sean Cronin, 17 Tom Court, 18 Donnacha Ryan, 19 Denis Leamy, 20 Eoin Reddan, 21 Jonathan Sexton, 22 Andrew Trimble
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