Coming off the bench in the second half in Pretoria, Mo'unga proved to be the All Blacks' saviour, slotting a conversion after the final whistle to steal the win after his side had been 30-13 down to the resurgent Springboks.
With Barrett having moved to fullback to accommodate Mo'unga's inclusion, debate has begun to arise as to whether or not the twice reigning World Player of the Year stay in the number 15 jersey, allowing for both stars to play at the same time though.
Speaking on Newstalk ZB this morning though, Carter said that the All Blacks need to persist with Barrett as the creative linchpin of the side.
"He's still the number one 10 but to have the competition with Richie there, and when the time is right in certain games for Beaudie to go to the back and Richie come on and add another string to the backline," he said.
"It's the kind of depth and competition you want in a squad.
"For me Beaudie is still the leader in that All Blacks side and what he's achieved in the last three or four years has been incredible."
Carter also praised Mo'unga's emergence as a genuine world class player, having steered the Crusaders to back to back Super Rugby titles.
"I'm extremely proud of Richie and the way he's progressed over the last couple of years. I worked with him down at the Crusaders and he's got such a clear head. He doesn't let pressure get to him as we saw in the weekend.
"The fact he's putting Beaudie under a lot of pressure is great."