It was a slow start to the second half-hour session as teams focused on pitstop practice for what is just the second refuelling round of the season.
That meant an early 1m14.124s from David Reynolds was enough to lead the way.
By the midway point of the session the times were well into the 1m13s, Cam Waters leading the way with a 1m13.518s.
That time almost made it to the end, only for Heimgartner to piece together an impressive two-lap stint to the flag.
The Kiwi, who was second fastest earlier today, jumped to the top with a 1m13.469s on the first of those two laps.
He then got the hard compound tyre to hold on for a second flyer as he lowered the benchmark to 1m13.419s.
"It shouldn't of [been faster on the second lap]," Heimgartner said. "The tyres were definitely better on the first lap.
"It's interesting, the track is evolving so fast. We managed to make some good changes that went with the track evolution. It's a nice weekend, we've got a solid base to start."
Practice 1 pacesetter Shane van Gisbergen was third fastest, a little over a tenth off the pace, followed by Chaz Mostert, Macauley Jones and Will Davison.
Bryce Fullwood capped of a great session for Brad Jones Racing with the seventh fastest time despite a scary rear-locking incident during an early practice stop.
"We had a bit of an issue," he explained. "Things weren't quite right, I couldn't quite stop properly. The brakes weren't quite working properly. It wasn't exactly part of the plan."
He wasn't the only driver to have issue getting into the box, Broc Feeney wiping out Triple Eight car controller Mark Dutton on one of his practice stops.
Todd Hazelwood was eighth fastest from Nick Percat and Scott Pye.
