Under fire for his form during the Super 12 season, Gregan emerged with two tries and man-of-the-match honours as the Australians piled on the points but left massive room for improvement with a near-record 45-16 thrashing.
Only a 46-10 belting in Brisbane four years ago outstripped the scoreline coach Eddie Jones was savouring in Perth.
"A pretty positive start," Jones said. "Ireland were pretty aggressive at the tackle, they contested lineouts, they came up quick out wide in defence. It was not a perfect start for us, but we were always going to be rusty and to a great extent we worked through that."
The Irish leaked errors and points hand-in-hand. They were also strangely vulnerable through the middle, an area the All Blacks and Springboks guard with impregnable pride.
Instead, the tourists directed their concentration to shutting down the Australians out wide. That was until on-field generals Gregan and five-eighth Elton Flatley held a meeting on the run, spotted the dangers and switched the point of the Australian ball-running.
It was disheartening for Wendell Sailor on the right wing - who may be in doubt for Saturday night's clash with Wales after injuring a rib - Joe Roff on the left touchline and debutant outside centre Morgan Turinui.
But it was also a welcome introduction for the Wallabies to what Jones described as a typically northern hemisphere pattern.
"It showed us how they are going to defend," he said. "They're playing this rush-up defence. (Ireland outside centre) Geordan Murphy was coming up strongly. It's not your traditional back-line play. It's like the old Bulldogs umbrella system in rugby league.
The Australians coped easily enough; they had the muscle in close to hammer through. Gregan was inspired, but he was also entitled to hand on accolades to a pack that frequently splintered the Irish forwards.
Second-rower Nathan Sharpe, No. 8 Toutai Kefu and flanker David Lyons brushed aside tacklers like they were swatting flies at camp in Coffs Harbour.
However, by shredding defenders with strength, the Australians were less inclined to rely on the creativity their coach wants them to develop for when they meet teams whose players hit like trucks, not gnats.
Inside centre Steve Kefu made several incisive runs, as did Flatley. But it was poor defence that contributed to their metre gains.
But it can be trite to be too critical. The Wallabies came up with six tries, two while Irish fullback Girvan Dempsey was in the sin bin.
Jones denied the Irish had gifted his side several of that half-dozen. He preferred to praise his side's defence for the turnovers they would capitalise on with five-point plays.
From a World Cup perspective, the most pleasing performance came from Flatley. He is not a gifted creative force like Larkham. But he is no stodgy stand-still distributor either.
His try after Irish rival David Humphreys had drifted too wide in defence was a clinical finish after spying opportunity. Earlier, Gregan took advantage of quick ball from his forwards. Sharpe and Kefu made the inroads and Gregan finished with a 20m dash from the back of the ruck.
Concerns for the Australians were the scrum, where tight-head prop Patricio Noriega was penalised three times in the first 20 minutes and his replacement, Ben Darwin, was also pinged for an indiscretion.The lineout had its moments and the kicking in general play was indifferent on occasions.
(Reproduced courtesy, The Sunday Times in Perth).