Rugby great Dan Carter weighs in on the battle for the All Blacks' number 10 jersey

The All Blacks greatest number 10 is backing incumbent Beauden Barrett in the first five-eighth role and says the pressure from within the squad is only a good thing.

Barrett was moved to fullback in the final quarter of the All Blacks' remarkable comeback win over South Africa in Pretoria on Sunday with rookie All Black Richie Mo'unga coming off the bench into first five-eighth position.

Mo'unga also took over the kicking duties from the two-time World Rugby player of the year which saw the Crusaders' number 10 kick the winning conversion to complete the 32-30 win.

In an interview with Newstalk ZB's Mike Yardley, Dan Carter said he was proud of the rise of former Crusaders teammate Mo'unga, who has played four tests this year, but added that Barrett remains the number one.

"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."

"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. To be the number one player in the world the last couple of seasons, he's been great on occasions this year. I think he's really trying to push himself in that leadership role. He's a key part of the All Blacks 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…it's a really fortunate position the coaches have got with quality players to be able to bring on as replacements and add a little bit too the game when needed. It's the kind of depth and competition you want in a squad.

The 36-year-old Carter is currently playing in Japan for the Kobelco Steelers as part of a two year deal.

"Playing here I guess is a little less pressure than when I was playing internationally and also in France so it's a nice change and I'm really enjoying it," he told Newstalk ZB.

"There's still a bit of physicality around the game. It is a little bit easier on your body but the game is played just so fast. The Japanese are extremely fit and they play the game with such speed and that's what they really pride themselves on. Even though your body isn't as battered after a game, your lungs are definitely tested."

He said the interest is starting to build ahead of the World Cup in Japan next year.

"It's growing. It's not a major sport here but I've been visiting here for the last 10 years and I've seen a huge growth in the sport. A lot of that was off the back of their amazing victory at the 2015 World Cup against South Africa. That really put rugby in the limelight here in Japan and obviously next year's World Cup, it's gone from strength to strength.

"All of a sudden you're seeing rugby players on billboards and magazines. We managed to sell out a club top league match the other week, so there is a lot more interest in rugby and I'm enjoying being part of that."