Mostert logged just nine laps in the second Fanatec GT World Challenge Australia powered by AWS practice session of the day.
The Arise Racing Ferrari 296 GT3 managed a best of 1:26.2569s, faster than Jayden Ojeda could go in the Mercedes-AMG GT3 by 0.0173s.
The fastest three runners were all separated by less than a tenth of a second, with Jaxon Evans logging in the second Arise Racing Ferrari just 0.0505s off Mostert’s lap.
Further, the fastest six times were separated by just 0.322s as all three manufacturers represented this weekend featured at the pointy end.
Rain lingered during the session leading to most teams running a limited programme.
New to the field this season, Mostert will team with 2023 series winner Liam Talbot and Ojeda has moved to Tigani Motorsport to join Paul Lucchitti.
The Grove Racing Mercedes-AMG GT3 was driven to fourth by Brenton Grove ahead of the Team BRM/ACM Finance Audi R8 LMS GT3 Evo 2 shared by Mark Rosser and Alex Peroni, while the all-New Zealand attack featuring Tim Miles partnered by Brendon Leitch was sixth in the Dayle ITM-supported entry.
The Triple Eight Race Engineering Mercedes-AMG GT3 of Peter Hackett and Declan Fraser placed ahead of Renee Gracie in the OnlyFans Team MPC Audi she will share with Paul Stokell, while the pacesetting Shaw & Partners/Kelso Electrical entry of Brad Schumacher and Will Brown was ninth.
Leading the Am Class was RAM Motorsport’s Mercedes-AMG GT3 shared by Michael Sheargold and Garth Walden just ahead of the Valmont Racing Audi for Marcel Zalloua sharing with Sergio Pires.
Ben Schoots was third in class for Black Wolf Motorsport in its category debut as the sole GT Trophy entry for KMB Motorsport pair Valentino Astuti and Michael Bailey split the Am Class in half by placing 13th outright.
Tony Bates enjoyed some running in his return after missing opening practice in the Ashley Seward Motorsport-prepared Mercedes-AMG to be fourth in class from James Koundouris in the Tigani Motorsport example.
The Audis of Ash Samadi and Marc Cini completed the field.
Qualifying for the Fanatec GT World Challenge Australia powered by AWS at Phillip Island begins tomorrow’s action at 10:35 AEST.