The brand new cars rolled out for the first of three 45-minute practice sessions on the tight, bumpy street course.
Predictably it was a cagey start as drivers gave the kerbs a wide berth, times initially languishing in the 1m15s.
Chaz Mostert was the first to set a representative time, the Walkinshaw Ford driver jumping to the top with a 1m13.313s at the five-minute mark.
The benchmark then steadily worked its way towards the 1m12s mark, the likes of Will Brown, David Reynolds, Nick Percat and Shane van Gisbergen all enjoying stints on top.
With eight minutes to go Mostert finally broke into the 1m12s with a 1m12.967s as he returned to the top.
Just two minutes later Heimgartner made a big step forward, skipping the 1m12s altogether as he vaulted to the top with a 1m11.995s.
His one-second margin didn't last long as the likes of Brown and Reynolds closed to within two-tenths on their next runs.
But there was no beating that Heimgartner time as the Kiwi made Supercars history by topping the first Gen3 session.
"We're undefeated so far," said Heimgartner, who also topped the recent pre-season test. "But it means absolutely nothing.
"In that session we were just going around. It's so different these cars, how they hit the kerbs.
"The confidence around this track to bleed off the brake and carry the speed, you need to build up to that, because if you misjudge that slightly you're in the wall.
"We won't really see a true indicative time until we get to qualifying and people can put a few sets [of tyres] on and try and extract that last half a second."
Brown and Reynolds ended up second and third while a late effort from Nick Percat saw him pip teammate Mostert to fourth.
James Golding was sixth fastest ahead of PremiAir Racing teammate Tim Slade, who was followed by Bryce Fullwood, Will Davison and Mark Winterbottom.
Neither Triple Eight car made the top 10, Shane van Gisbergen 11th fastest and Broc Feeney 20th.
All four Tickford cars missed the 10 as well, Cam Waters best-placed down in 19th as James Courtney, Declan Fraser and Thomas Randle finished right down the bottom of the order.
Practice continues with a second session at 1:45pm local time.
