The hour-long session began in the driest conditions seen since the third session on Friday morning.
There were no Hollywood times out of the gate, however, as the teams concentrated on pit practice with driver changes and brakes.
Boys set the representative first time with a 2m11.770s a few minutes before Alex Davison took over with a 2m10.340s.
David Reynolds then plunged into nines and then eights with a time of 2m08.562s just before he overbraked at The Chase and went off.
Dale Wood beat Reynolds’ time at the 12-minute mark, only for Chaz Mostert to come out a few minutes later and set a time of 2m07.204s.
At 20 minutes the times changed to six when Will Davison, who had taken over the #17 DJR Ford from his brother, set a time of 2m06.804s.
Times continued to improve as the session neared the halfway point, Shane van Gisbergen lapping in 2m06.406s while Anton De Pasquale dropped to second on 2m06.667s.
The next improvement came from Mostert with a time of 2m06.165s just into the half hour mark, which remained the benchmark until Shootout simulations began later in the session.
Those ranked sims started with around 10 minutes to go when Davison jumped out on top with 2m05.630s. At the same time, his DJR teammate Anton De Pasquale was second fastest with 2m06.032s.
With two minutes to go, van Gisbergen passed Davison in 2m05.613s only for Mostert to go faster again in 2m05.510s.
That was the fastest anyone went thanks to a red flag that interrupted the session at the last minute.
The culprit was Boys, who hit the wall on the metal rack and damaged the Brad Jones Racing Holden that the team stayed up late repairing after their qualifying encounter with van Gisbergen yesterday.
That left Mostert in first place ahead of van Gisbergen and Davison, who was a lap down when the red flag appeared.
“It’s never perfect, you know us racing drivers, we always like to keep fine-tuning,” Mostert said. “But for me that session was the happiest of the whole weekend, wet, dry or whatever.
“We’ve been fine-tuning the car and getting it a little bit closer to the window we need for this weekend.”
Provisional pole winner Cam Waters was fourth fastest ahead of Reynolds, De Pasquale and Brodie Kostecki.
Mark Winterbottom, Lee Holdsworth and Scott Pye rounded out the Top 10.
The Blanchard Racing Team Mustang, which will start tomorrow’s race from last place, has not completed a single lap in the session.
That was thanks to an issue with the hanging jacks damaging the car as it left the garage for its first run.
The first five rows of the grid will be determined by the Top 10 Shootout, which begins at 5:05 pm local time.