Gregory has enjoyed a meteoric rise after initially missing out on the squad, however he has made the most of his opportunities to earn the right to start.
He said he's learned a lot out on the park playing for the Baby Blacks.
"I learned just to be myself out there and not let the big moments get to you," he said.
"People can let it fluster them but you've got to remember you've played a thousand games before.
"We've tried to put [winning the 2017 World Cup] aside. It's a new year and we've got a new group so we're just focused on what we can do when we get there."
Coach Craig Philpot said coming up against Australia in their final pool match is an exciting prospect.
"It's all or nothing for Australia; they need to win to progress," he said.
"It's really important for us to absorb early pressure, play the game at the right end of the field and push that pressure back on them. If we force them to play their hand it will create some opportunities for us."
Other changes see Caleb Clarke return to the wing after missing the Wales match with a virus, while prop Tevita Mafileo and lock John Akau'ola-Laula have been rewarded with starting spots after impressive outings off the bench.
Flanker Waimana Riedlinger-Kapa and halfback Jay Renton also get starts.
The game kicks off at 7am (NZ time).
New Zealand: Vilimoni Koroi, Bailyn Sullivan, Billy Proctor, Scott Gregory, Caleb Clarke, Harry Plummer, Jay Renton, Devan Flanders, Tom Christie (c), Waimana Riedlinger-Kapa, John Akau'ola-Laula, Laghlan McWhannell, Tevita Mafileo, Flynn Thomas, Rob Cobb. Reserves: Kaliopasi Uluilakepa, Xavier Numia, Sione Asi, Will Tucker, Hoskins Sotutu, Xavier Roe, Kaleb Trask, Jamie Spowart.
