Erebus Motorsport rookie Will Brown was top of the time sheets after the morning runs in official pre-season testing at Winton.
The 22-year-old set a 1:19.5089s flyer on the hour mark aboard his #99 Commodore.
Like Matt Stone Racing's Zane Goddard at Queensland Raceway last week, Brown's lap could stand the test of the day as heat encased the Victorian circuit.
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Brown managed to set his lap just after 1000 local time, with the temperature rising to 26 degrees by midday.
A high of 31 is expected for the afternoon.
Brown pipped former Erebus driver David Reynolds, who set the early running.
Kelly Grove Racing recruit Reynolds clocked a 1:20.0714s on his eighth lap of the morning.
The 2017 Bathurst winner was just 0.1232s ahead of Tickford Racing's Cameron Waters before Brown lowered the marker.
The #20 DEWALT Commodore of Scott Pye was the mileage king through two-and-a-half hours, with the Team 18 entry recording 60 laps.
Pye did suffer an off at Turn 5 in the first hour, but he safely rejoined after traversing the infield.
The 31-year-old, who was one of the surprise packages of 2020, was third on a 1:20.0987s, just 0.0273s down on Reynolds.
Tickford duo Waters and Jack Le Brocq registered 50 laps each to midday.
Ninth-placed James Courtney, aboard the #44 Boost Mobile Tickford Mustang, was last of the cars within a second of Brown's time.
The 2021 season will commence at the Repco Mt Panorama 500 next weekend.
Tickets for the event are on sale now.