Brodie Kostecki led the way in opening practice for Round 6 of the Dunlop Super2 Series at the Supercheap Auto Bathurst 1000.
Thursday's sole Super2 session ahead of Saturday's 250km race was run in wet conditions at Mount Panorama.
Fresh from taking a maiden Super2 victory at Sandown, Kostecki turned a 2:33.8141s in the final minute to shade Macauley Jones by 0.0756 seconds.
Kostecki and Jones traded top spot during the closing stages of the 40-minute session, Kostecki taking the lead first, then Jones and ultimately Kostecki again.
Eggleston Motorsport's Will Brown was third, having led the field early, two tenths adrift.
MW Motorsport driver and 2016 Super2 champ Garry Jacobson was fourth, followed by Thomas Randle who was fastest of the rookies and also spent time at the top.
Holden pair Dominic Storey and Jack Smith filled the next two spots, followed by Dean Fiore in the second MW Nissan, while Alex Rullo was only 21st in the third.
Kurt Kostecki was ninth, ahead of Garry Rogers Motorsport pair Mason Barbera and Chris Pither and series leader Paul Dumbrell.
Two-time Le Mans winner Earl Bamber is pairing his Bathurst Supercars campaign with Shane van Gisbergen with a Super2 outing alongside Brenton Grove.
Bamber started the session in the ex-Triple Eight Commodore, Grove taking over after 15 minutes and setting the time that left them 17th.
Within the top 10, Jones, Brown, Jacobson and Fiore are on double duties with Bathurst's Great Race, along with Pither, Dumbrell, Bryce Fullwood (15th in practice) and Bamber.
Practice 2 will take place 10:20am on Friday, followed by ARMOR ALL Qualifying that afternoon.