Conditions steadily improved during the half-hour session as the likes of Tim Slade, Chaz Mostert and Macauley Jones were at the forefront of time.
Heimgartner made his first appearance in P1 shortly after halfway through the session after switching to slick tires before being mixed in order as the track got faster.
The Kelly Grove Racing driver then ran a green tire run in the final minutes, a late rain shower wasn’t enough to keep him from regaining first place in 1: 49.241 seconds
“We went green very late,” said Heimgartner.
“The car was good, I knew I could create the time. I could drive a little faster again, but I made a few small mistakes that cost a couple of tenths.
“But I’m really happy. We picked up the car this weekend where we were last year. So I really know what I’m up to, which is half the battle. Under these conditions, you want to know what you’ve got . “
Jamie Whincup, who was second fastest, said he was surprised at how quickly the track dried between those showers.
“Today it was about rain – the track is starting to dry up and it’s raining again,” said the seven-time series champion.
“It will probably go on for the rest of the day, but my car is reasonable under both conditions.
“It will be who drives with the right tires at the right time for qualifying, but if we can do it right, we should be close.”
“The track is pretty slippery and it’s not that hot here, which traditionally means it would dry slowly, but if you don’t get a little rain it actually dries faster than expected. We are monitoring this and hope that we put on the right tires at the right time. “
Will Davison and David Reynolds were third and fourth fastest, ahead of Chaz Mostert and James Courtney.
Todd Hazelwood finished seventh, series leader Shane van Gisbergen eighth, Brodie Kostecki ninth and Bryce Fullwood tenth.
