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Mo'unga was instrumental for the Crusaders as they beat South Africa's Lions 37-18 in Christchurch on Saturday to successfully defend their title and grab a ninth overall.
While the win was built on defence, 24-year-old Mo'unga ensured the scoreboard ticked over to build pressure on the visitors, who dominated possession and territory.
He was flawless off the tee with three penalties and four conversions, challenged the defence with his running and passing, and made the right tactical decisions after a shaky start.
Such was the assuredness of his performance it was hard to remember that he had played just 10 minutes off the bench in one test against France last month, while his Lions counterpart Elton Jantjies had made 26 appearances for the Springboks.
It was the second successive week Mo'unga had outplayed an international first five. Pundits raved about how he had made two-time World Player of the Year Barrett look second best in the semi-final last week.
Crusaders coach Scott Robertson was effusive about Mo'unga's performance in the final but felt his attacking and tactical attributes were not what made him stand out.
"What I like about Richie is that he is brave on defence," Robertson told reporters. "That is the biggest part of his game.
"He had great feet and great hands and could kick clutch penalties and conversions.
"Now he is brave on D (defence), you have to have the whole skill set to play test rugby and he showed he could do that."
Mo'unga, who missed two months this year after having surgery on a broken jaw, is almost certain to be named in Steve Hansen's Rugby Championship squad on Monday, with Barrett and utility back Damian McKenzie as the other first five options.
Despite being compared to All Blacks great Dan Carter by both Robertson and former Crusaders assistant coach Leon MacDonald, it remains unlikely he will dislodge Barrett from the number 10 jersey just yet.
Barrett, after all, has played 64 tests for the All Blacks, half of which have been as the starting first five. He won his two Player of the Year awards since succeeding Carter after the 2015 Rugby World Cup.
Hansen also played down the Mo'unga hype, warning pundits and one-eyed Cantabrians not to get too excited until the player was truly tested.
"He's playing behind a Rolls Royce pack," said Hansen.
"He's playing the way we're expecting him to play behind a pack like that.
"It's going to be really interesting to see how he does in a big game."