Lolesio will start at flyhalf with club teammate Irae Simone at inside centre for a must-win showdown against the All Blacks on Saturday night.

They will step onto Sydney Olympic Park with zero Test caps between them, carrying the hopes of Australian rugby fans as they replace injured duo James O'Connor and Matt To'omua who have played 54 Tests apiece.

It marks the first time a Wallabies 10-12 pairing have debuted alongside each other in 35 years, yet those who know the duo say they will not be overawed by the occasion.

A quick glance at 20-year-old Lolesio's resume suggests as much. ACT Brumbies coach Dan McKellar recalls a time this kid asked, tongue in cheek, "what's pressure?"

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But ask him if he has always been this cool, calm and collected, and the answer is somewhat surprising.

"I'm going to be completely honest, not really, no. I've learnt a lot growing up. When I was very young I had a pretty hot head, I'd always ... I can't really swear can I? I'd always get angry at myself if I made a mistake," Lolesio said.

"I don't know, ever since I moved to Canberra I started playing 10. I realised, playing against men, if you've got the keys and you're playing in that position, you've got to be nice and calm, and be assertive with your words.

"I've learnt that a lot during my time in Canberra, and it just clicked. I don't really think about it too much to be honest, I just thought about the task at hand.

"I remember the first pre-season training I had at Brums when I was a 17-year-old, Dan came up to me after a session and he was just like 'which position do you prefer, 10 or 12?'

"I was just straight up like 'I don't really care'. He told me after that training session, 'I reckon you're a 10, mate', and it's probably lucky he said that, he's probably happy he said that."

Because Lolesio wore No. 10 when he overcame a two-month injury layoff to guide the Brumbies to the Super Rugby AU crown with a man of the match performance in the grand final last month.

While the lights were shining a little brighter this time around, it was reminiscent of the day Lolesio claimed best afield honours after leading Nick Scrivener's Tuggeranong Vikings to a thrilling John I Dent Cup triumph in 2018.

Or the time, little more than a year later, he nailed a sideline conversion after the siren to send the Canberra Vikings to the National Rugby Championship decider.

Talk of the Auckland-born playmaker pulling on a Wallabies jersey was often a matter of when, not if. It seemed that moment would come in the Bledisloe Cup series opener.

Instead he was forced to watch 89 gruelling minutes from the bench with O'Connor and To'omua left to pull the strings before the match finished in a draw.

"It was probably the biggest build-up of my life to be honest," Lolesio said.

"It was disappointing at the start, but I'm not too fussed by it. I know I've got a lot of opportunities ahead of me.

"When I get this chance to start, I'll be ready. That's all I know. When this opportunity comes, I'll grab it by the horns."

TRI-NATIONS | BLEDISLOE CUP

Saturday: Australia v New Zealand at Sydney Olympic Park, 7.45pm.

Wallabies squad: 1. James Slipper 2. Brandon Paenga-Amosa 3. Allan Alaalatoa 4. Lukhan Salakaia-Loto 5. Matt Philip 6. Ned Hanigan 7. Michael Hooper (c) 8. Harry Wilson 9. Nic White 10. Noah Lolesio 11. Marika Koroibete 12. Irae Simone 13. Jordan Petaia 14. Filipo Daugunu 15. Dane Haylett-Petty. Replacements: 16. Jordan Uelese, 17. Scott Sio, 18. Taniela Tupou, 19. Rob Simmons, 20. Fraser McReight, 21. Tate McDermott, 22. Reece Hodge, 23. Hunter Paisami.

All Blacks squad: 1. Karl Tu'inukuafe, 2. Dane Coles, 3. Ofa Tuungafasi, 4. Patrick Tuipulotu, 5. Samuel Whitelock, 6. Shannon Frizell, 7. Sam Cane (c), 8. Hoskins Sotutu, 9. Aaron Smith, 10. Richie Mo'unga, 11. Caleb Clarke, 12. Jack Goodhue, 13. Anton Lienert-Brown, 14. Jordie Barrett, 15. Beauden Barrett. Replacements: 16. Codie Taylor, 17. Alex Hodgman, 18. Tyrel Lomax, 19. Scott Barrett, 20. Dalton Papalii, 21. TJ Perenara, 22. Ngani Laumape, 23. Rieko Ioane.