Teamed with karter Adam Mercer, Mostert ended up the best of the Supercars runners in sixth, with van Gisbergen and Super2 driver Kurt Kostecki 13th, Courtney's entry 14th and Hazelwood failing to finish.
It marked a karting return of sorts for Courtney, who won world karting titles in 1995 and '97 before switching to cars.
Over at Winton, Tim Slade took on two grassroots enduro events; the Excel Enduro Cup, contested over two 90-minute races, and the HQ 4 Hour Enduro.
In the Excels, Slade teamed with his father Gil, finishing 11th and eighth in a field that also featured Steven and Jett Johnson, racing together for the first time.
Tim Slade earlier raced alongside Lee Holdsworth’s brother Brett in the HQs, ending the single four-hour contest in fourth place.
Heimgartner proved too good at Pukekohe. pic: BNT V8s
In New Zealand, Andre Heimgartner made a successful return to the BNT V8 Series at Pukekohe, driving a Hamilton Motorsports VE-model Holden Commodore.
Heimgartner, who will run the whole series with the squad over the summer, won the opening two races before the final was abandoned due to wet weather.
Meanwhile in Melbourne, Scott McLaughlin, Cameron Waters and Michael Caruso took part in a celebrity race at the Aus-X Open supercross event.
A week after being crowned Supercars champion for the second time, McLaughlin made a less than successful supercross cameo, finishing last after a miscue at the first corner.