Todd Kelly jumped from 20th to an eventual third in the final minutes aboard his Nissan ahead of Fabian Coulthard, Michael Caruso and Sandown winner Cameron Waters.
The session was the first chance for the teams to readjust to the 2016 Dunlop tyres, which the field has reverted to for the punishing Bathurst circuit.
Mostert’s time proved nearly 0.4s slower than the fastest Practice 1 time from 12 months ago .
“It felt a little bit nervous out there to start with, but it feels pretty good out of the box,” said Mostert.
“You’ve got to give the new [set-up] stuff we’ve been doing a crack [on the 2016 tyre], and the car seemed to be OK.
“The first thing out there, you feel the braking stability and sidewall movement compared to the new [tyre], and you kind of think, ‘what’s happened with the car?’, but you’ve just got to delete the previous round and try to remember what happened last year.
“I’m pretty happy, we’ll see how the rest of the weekend goes.”
The session’s big story was a crash for Tim Slade, who smacked the concrete heavily in The Esses at the 32-minute mark, at which point he’d been fastest on 2:07.095s.
Slade lost the rear of the Freightliner entry through the left-hander, grazing the right-side wall with the back of Commodore before making heavy contact on the left.
The crash has left Brad Jones Racing with another major repair, with the car not expected to return to the track until tomorrow.
Co-driver Ash Walsh is cross-entered in the sister Nick Percat/Macauley Jones entry, and will likely drive the #8 car in today’s second session to assess his fitness.