The one aspect that the Barrett-Mo'unga battle could come down to

All Blacks legend Sir John Kirwan believes the battle between Richie Mo'unga and Beauden Barrett for the All Blacks No 10 jersey could come down to the goal-kicking of the latter.

Barrett has been afforded an extended run of game time in his preferred position after Mo'unga, New Zealand's incumbent pivot, joined Sam Whitelock and Aaron Smith in opting against travelling to Australia last month ahead of the arrivals of their respective children.

As a result, Barrett - who struggled for game time at first-five in test rugby throughout 2019, 2020 and the early part of this year - was handed the starting honours at No 10 in the All Blacks' first two Australian-based Rugby Championship tests.

Barrett starred in both matches against the Wallabies in Perth and Los Pumas on the Gold Coast this month as the All Blacks romped to successive victories to establish themselves as firm Rugby Championship favourites.

However, Mo'unga, who has dominated the No 10 jersey since 2019, arrived in Queensland on Tuesday and has begun his two-week quarantine to rejoin the All Blacks squad ahead of their second test against the Springboks on the Gold Coast on October 2.

That presents a selection dilemma for All Blacks head coach Ian Foster, who looked set on Mo'unga as his first-choice playmaker prior to his decision to remain in New Zealand.

The form of Barrett, though, may have turned Foster's head, and with two tests still to play against Los Pumas and the Springboks before Mo'unga is next available, the former is set for more opportunities to state his case for future starting roles at No 10.

Speaking on The Breakdown, Kirwan, the former World Cup-winning All Blacks wing, said there is so little to pick between the pair that who starts once Mo'unga links back up with the squad could depend on Barrett's goal-kicking form.

While his on-field exploits have dazzled in recent weeks, the two-time World Rugby Player of the Year endured a turbulent time off the kicking tee against the Wallabies and Los Pumas.

In the Australian test at Optus Stadium, Barrett had a goal-kicking success rate of just 50 percent as he slotted three of his six attempts, with two of his missed attempts coming from point-blank range.

Injury then plagued him in the clash against Argentina as a calf cramp saw younger brother and fullback Jordie assume the goal-kicking duties from the end of the first half onwards.

For all the value he has provided as an attacking threat with ball in hand, Barrett is still yet to prove his worth as a reliable goal-kicker for the All Blacks this year, and, according to Kirwan, that could be the difference when it comes time to choosing between him and Mo'unga.

"When we talk about leadership, the interesting thing for me about Beauden Barrett is will this selection come down to kicking?" Kirwan asked The Breakdown as he compared Barrett's speed and attacking prowess to Mo'unga's hot-stepping ability.

"Is that his only worry at the moment? Because, when you talk about Mo’unga, yeah, he’s x-factor, but so is Barrett. They have very different styles of play, but they both have this ability to change a game.

"That seeing a gap and just accelerating through it, which is a lot harder than it looks because those gaps close pretty quick, and then that out-the-back hand," Kirwan said in reference to Barrett's spectacular pass to set-up Luke Jacobson's try against Argentina.

"Mo’unga does the stepping stuff, so I think Beauden will be out kicking as much as he can because that’s what it might come down to when Mo’unga does turn up.”

Foster dismissed concerns over Barrett's goal-kicking ability in the wake of the Perth test as he backed his star man to make amends for his lacklustre efforts off the tee over the coming weeks.

“Clearly it wasn’t the night for either kickers, but, particularly in Beaudy’s case, if he had to get one of the two things right of goal-kicking or playing really well, I’m really pleased he got the right one right," Foster said at the time.

“I thought he handled the game really, really well. Great decision-making, particularly early, and really calm when we were under a bit of pressure with the [red] card [against Jordie Barrett].

“I think he showed his class. The goal-kicking will come right.”

Ex-All Blacks utility back Mils Muliaina praised Barrett's return to form, but told The Breakdown that patience is required before the 95-test international is back to his best after spending the first half of this year in Japan's Top League.

"You’ve got to realise how big a step that is coming from Japan and then get yourself into the All Black environment, finding his feet, getting used to the intensity, not just of trainings, but also the match, getting up to that mental state, preparing week-in, week-out," Muliaina said.

"I think he’s just starting to find his feet. He’s got some good leaders around him, in terms of Brodie Retallick and the young guys, like Rieko Ioane, that are really stepping up."

Muliaina, an All Blacks centurion and former World Cup-winner, added that Barrett's performances have been all the more impressive given the absence of Mo'unga, Smith and Whitelock.

"You’ve got to remember, also, what a chunk of experience we’ve had to leave at home that still are going to join the side, so, when you’re looking from Beauden Barrett’s point-of-view, he’s just starting to get into the flow of things in terms of his game.

"That try that he set-up, that magical pass, that’s just out-and-out class, isn’t it? It’s nice to see those moments, but also him be able to tighten things up and talk to his forwards and run the cutter.

"That certainly needed to be done yesterday against the Pumas because it was starting to get a little bit scrappy, particularly in that first part of that first half."

Kirwan, meanwhile, was impressed with a number of other players in New Zealand's 39-0 thumping of Argentina at Cbus Super Stadium on Sunday.

The former Italy, Japan and Blues head coach pinpointed inexperienced hookers Asafo Aumua and Samisoni Taukei'aho, lock Scott Barrett and loose forwards Dalton Papalii and Luke Jacobson as the standouts in their side's dominant victory.

"Taukei’aho, he’s like a big Keven Mealamu. Asafo was awesome as well, and I’m just thinking, ‘This guy [Taukei'aho] comes on, he’s a kid, and he starts bashing people up’. I really enjoyed that, so I think our depth is good," Kirwan said.

"I agree with Ruby [Tui, Tokyo Olympics gold medallist and fellow panellist], it’s who we didn’t really see that I was impressed with.

"Scott Barrett, I mean he just muscled up. We talk about [Brodie] Retallick a lot, but I think he’s [Barrett’s] finally understood his role as a lock.

"He’s not getting out there, he’s carrying when he needs to, but he’s just bashing people and carrying hard, just doing that gritty work, and then, at one stage, I was thinking, ‘How good is Dalton Papalii?’, because I haven’t seen him.

"Then, all of a sudden, turnover, and so I think what Ruby talks about when you get that balance right, when someone’s a bit looser, someone’s really tight - Jacobson, I thought, unbelievable - so the depth is there, and then we’ve got all this leadership to come back in."

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