"Paddy and Brian know one another for 10 or 11 years. At Under-19 level, they played next to one another," Kidney explained.
"I would respect everybody's views as to what way we've picked. But to play Brian and Luke (Fitzgerald) there would have meant changing their positions from a month ago, and maybe changing somebody into the left wing position and someone else into full-back.
"There's always a different risk management thing to be calculated as to who you bring through.
"But I would have confidence in them playing. With the way we chop and change at training, sure you'd never know what shape the back-line would be at any one minute and that's just the way the game is going."
Fitzgerald, O'Driscoll's centre partner for the GUINNESS Series in November, has been switched out to the left wing and though full-back Rob Kearney went over on his ankle at training today (Tuesday), Kidney is remaining positive about his fitness.
"Just as a precaution to take the weight off it, Rob's on crutches. I've no news on that but I'd imagine he'll be alright.
"These things happen, especially on Tuesdays when we're inclined to do contact."
Expanding on his decision to select Wallace at inside centre, the Corkman added: "Like a lot of the lads, Paddy's playing there (at inside centre) and playing well.
"All the lads, in the back-line, have been playing in those positions by and large. So why change them from that? Give them a run together in those positions.
"Luke has been playing on the left wing for the last couple of games, Brian at 13, Paddy at 12 and Rob at 15. I felt that they were going well and that I'd leave them there."
Asked about Wallace's qualities as a player and what he feels he can bring to Saturday's game, the Irish coach immediately pointed to his recent form with Ulster and his adaptability in that he has played at out-half for both province and country before.
"Paddy's shown a lot of consistent form, he dovetails well both with Brian and Ronan (O'Gara) on the inside and outside. Obviously he's played 10 before and that means you sorta have two five-eighths.
"He has a good temperament, and I like that in the way that he can bring that to the game. He would have a feel for what the out-half is going through and he can lean in to take the pressure off him.
"And at the same time, the fact that himself and Brian have been linking with another for a 10 or 11-year period. He's playing well and I think he certainly deserves a go."
Ahead of his first RBS 6 Nations game as a head coach, Kidney admitted that he and his coaching staff had some tough decisions to mull over and that 'we've had to leave a lot of quality guys out.'
"Girvan (Dempsey) isn't in the 22, Geordan (Murphy), who is on the bench, played well for us against Argentina and is playing well.
"I wouldn't be a huge fan of man-of-the-matches but I was at two games there recently on the one weekend that Geordan got man-of-the-match in the Leicester-Ospreys match and then Rob turns around and gets it in the Leinster-Edinburgh game.
"They're both playing well but I just felt the mix was better to have Rob there at full-back."
Gordon D'Arcy has also made a welcome return to the Ireland squad after recovering from a serious arm injury. He has won a place on the bench and Kidney is pleased with the progress he has made since his long lay-off.
"Gordon's been coming through matches. He's played a bit on the right wing lately and he played for Lansdowne in the AIB League last weekend - that was his first game at 12 since he's come back.
"It would be unfair on him when he's all but 12 months out of the game to just throw him back in.
"It would be unfair on Paddy too because Paddy's been going nicely. Again, that's the benefit of the bench and let's see how it goes as regards when guys come in."
Meanwhile, Keith Earls, who made his Test debut during the GUINNESS Series, is fighting his way back to fitness after sustaining a dead leg in action for Munster against Montauban recently.
"Keith Earls wasn't considered because the bang he got there recently hadn't cleared up for him to be in the reckoning for either the senior or 'A' team. There's an outside possibility he'll be available for the following week," Kidney said.