The flanker, one of just two uncapped players in the 36-strong squad, surged into calculations after injury to pivotal backrower Rob Valetini and the in-form Langi Gleeson.
Hulking lock Will Skelton, who missed the Fiji Test with a calf niggle, remains sidelined in another huge blow to the underdogs.
Schmidt said all three were nearing full fitness and expects them to be available for next Saturday's second Test in Melbourne.
Canberra-raised Champion de Crespigny returned from a Top 14 stint with Castres Olympique to play for the Western Force this season to join the back of a bulging queue of contenders.
But, with two-time defending John Eales Medallist Valetini and Gleeson on ice - former captain Liam Wright (shoulder) is also out of the picture - he'll be asked to dent a Lions line that has enjoyed five relatively comfortable wins since arriving in the country late last month.
"Big shoes to fill," Schmidt said of the debutant, who brings an aerial threat at lineouts and starch on either side of the ball.
"He was on the radar (12 months ago). Not necessarily right in the middle, but in the periphery and got a little bit closer as the season wound on."
Backrow partner Fraser McReight was less diplomatic.
"He's a psycho; loves contact and ready to go," the No.7 said.
"Loves the physical nature of the game. I've heard all the stories from the Force boys."
The coach also backed "quietly confident" 22-year-old Tom Lynagh to steer the ship in a new-look halves combination with Jake Gordon.
Ben Donaldson will provide backline back-up on the bench, with Schmidt resisting the temptation to recall veteran James O'Connor, who wore the No.10 in all three Tests 12 years ago.
Hooker Matt Faessler returns after a last-start hat-trick in gold, having started for the Reds instead of playing against Fiji in his comeback from a hamstring injury.
Andrew Kellaway has bumped Filipo Daugunu off a new-look bench that includes hooker Billy Pollard, scrumhalf Tate McDermott, prop Tom Robertson and flankers Tom Hooper and Carlo Tizzano.
James Slipper will join George Smith as the only Wallabies to feature in back-to-back Lions series in the professional era while No.8 Harry Wilson has retained the captaincy.
Lynagh hasn't played since the Reds lost their Super Rugby quarter-final in early June, with a broken hand ruling him out of the Fiji Test.
The Italy-born, England-raised playmaker finished school and moved to Australia in 2021 and has flourished under Wallabies coach-in-waiting Les Kiss as the Queensland Reds' main man for the last two years.
He'll make Australian rugby history as the first father-son Wallabies to face the Lions after Michael Lynagh wore the No.10 against the Lions in 1989.
English lock Maro Itoje will captain a Lions side that had no room for exciting flanker Henry Pollock, in-form Welsh backrower Jac Morgan or coach Andy Farrell's son, Owen.
WALLABIES: James Slipper, Matt Faessler, Allan Alaalatoa, Nick Frost, Jeremy Williams, Nick Champion de Crespigny, Fraser McReight, Harry Wilson (c), Jake Gordon, Tom Lynagh, Harry Potter, Len Ikitau, Joseph-Aukuso Suaalii, Max Jorgensen, Tom Wright. Bench: Billy Pollard, Angus Bell, Tom Robertson, Tom Hooper, Carlo Tizzano, Tate McDermott, Ben Donaldson, Andrew Kellaway.
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