McLaughlin ran green tyres quite early in the session, the benchmark time – a 1m15.201s – coming just eight minutes in to the half-hour hit-out.
He then went for a second qualifying simulation later in the session, but despite a purple first sector was unable to match his earlier time.
"That's one thing we've brought on since Townsville," said McLaughlin about running two sets of greens. "We need to get comfortable with our qualifying, knowing that we need to qualify at the front and that's half our job done.
"Overall I'm really happy, the car was really balanced. I'm really enjoying the new circuit, the West circuit is enjoyable. It's a new challenge."
Mostert ended up second by just 0.09s, his time also coming earlier in the session after he ran wide at the last corner on his final qualifying sim.
Fabian Coulthard was third fastest followed by Bryce Fullwood, Anton De Pasquale and Nick Percat.
It was a quiet showing from the Triple Eight Holdens, meanwhile, title contender Whincup the best of the Red Bull cars down in eighth.
Shane van Gisbergen was just 17th quickest, a lock-up late in the session proving costly.
| Cla | # | Driver | Time | Gap | Interval |
|---|---|---|---|---|---|
| 1 | 17 |  Scott McLaughlin | 1'15.201 | ||
| 2 | 25 |  Chaz Mostert | 1'15.293 | 0.092 | 0.092 |
| 3 | 12 | Fabian Coulthard | 1'15.346 | 0.145 | 0.053 |
| 4 | 2 | Bryce Fullwood | 1'15.410 | 0.209 | 0.063 |
| 5 | 20 | Scott Pye | 1'15.461 | 0.260 | 0.050 |
| 6 | 99 | Anton De Pasquale | 1'15.525 | 0.323 | 0.063 |
| 7 | 8 | Nick Percat | 1'15.536 | 0.335 | 0.011 |
| 8 | 88 | Jamie Whincup | 1'15.586 | 0.385 | 0.050 |
| 9 | 14 | Todd Hazelwood | 1'15.599 | 0.397 | 0.012 |
| 10 | 7 | Andre Heimgartner | 1'15.625 | 0.424 | 0.026 |
| 11 | 55 | Jack Le Brocq | 1'15.655 | 0.453 | 0.029 |
| 12 | 15 | Rick Kelly | 1'15.694 | 0.493 | 0.039 |
| 13 | 5 | Lee Holdsworth | 1'15.721 | 0.520 | 0.026 |
| 14 | 44 | James Courtney | 1'15.756 | 0.555 | 0.035 |
| 15 | 18 | Mark Winterbottom | 1'15.786 | 0.585 | 0.029 |
| 16 | 6 | Cameron Waters | 1'15.804 | 0.602 | 0.017 |
| 17 | 97 | Shane van Gisbergen | 1'15.859 | 0.658 | 0.055 |
| 18 | 3 | Macauley Jones | 1'15.865 | 0.663 | 0.005 |
| 19 | 9 | David Reynolds | 1'15.883 | 0.681 | 0.017 |
| 20 | 4 | Jack Smith | 1'15.976 | 0.774 | 0.093 |
| 21 | 34 | Jake Kostecki | 1'15.978 | 0.777 | 0.002 |
| 22 | 19 | Alex Davison | 1'16.019 | 0.818 | 0.041 |
| 23 | 22 | Chris Pither | 1'16.101 | 0.899 | 0.081 |
| 24 | 35 | Garry Jacobson | 1'16.105 | 0.904 | 0.004 |
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