They were well known to one another on the Christchurch First XV scene a few years back with McKenzie at Christ's College and Mo'unga at St Andrew's.
They were also both in the 2014 New Zealand Under-20 side and here they are now both desperate to prove their worth as the All Blacks' key playmaker and take possession of that No10 shirt.
Potentially it could have been tense and negative but Mo'unga and McKenzie appear to have been like Aaron Cruden, Barrett and Colin Slade before them and put aside all personal disappointments and ambition to help each other become better players and the All Blacks a better team.
It is a good opportunity for him to grow and learn from the lessons from the last game.
"We really push each other at training and that is the beauty of this team," said Mo'unga.
"Every week you are striving to be your best and every week I am pushing Damian and he knows that and he is pushing me, too.
"That grows the team and that grows the individual I think and as much as I would like to be starting I am really happy for Dmac and I know he is going to do a great job."
And the reality for McKenzie is that he is, indeed, going to have to do a great job to stay ahead of Mo'unga in the All Blacks' pecking order.
He was handed a tough assignment last week in Wellington, injected into the game after just 12 minutes behind an All Blacks pack that was failing to deliver the right attacking platform.
There was also a mindset among his peers that they needed to push the ball wide quickly to exploit the numerical advantage they held as a result of France having been shown a red card.
As much as there were mitigating circumstances, McKenzie contributed to some of the All Blacks' untidiness and uncertainty by not delivering the desired sort of authoritative game management the coaches were looking for.
Having played so much of his professional football at fullback, game management and tactical leadership are weaknesses in McKenzie's game.
He's a brilliant line runner, a clever distributor and creator of space for others and his instinctive brilliance is compelling.
The coaches want him to display all those qualities but around a more structured framework of having put the All Blacks into the right places on the field.
Conversely, game management is Mo'unga's key strength.
Their need to continue to cooperate will intensify.
It's a point All Blacks head coach Hansen hinted at when he revealed, indirectly, how close the two men are in the pecking order.
"If it had gone the other way it would have been because we wanted Damian to be available to play fullback as well," said Hansen.
"For this one, we have made the decision that we want him to be a guy who can play first-five for us.
"So we decided we would take Damian at first-five which meant we needed Jordie at fullback. It is a good opportunity for him to grow and learn from the lessons from the last game."
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