Chaz Mostert set the fastest time in an opening Supercars practice session at Sydney Motorsport Park that ended in wet conditions.

Rain arrived at the Western Sydney venue with five minutes of the hour long run remaining, ensuring there’d be no late improvers.

Mostert was one of several to perform initial balance checks on hard tyres before switching to the soft.

The Supercheap Ford went to the top of the order with 1:30.33s just past the halfway mark, knocking previous fast-man Michael Caruso to second.

Brad Jones Racing’s Tim Slade eventually split the pair shortly before the rain.

Volvo’s Scott McLaughlin made it four manufacturers in the top four ahead of Rick Kelly, Jamie Whincup, James Moffat, Shane van Gisbergen, James Courtney and Mark Winterbottom.

This weekend marks 12 months since Mostert’s last race win, which came amid a hot streak of form for the youngster prior to his Bathurst crash.

Largely struggling for race pace during the season to date, Mostert is optimistic that developments trialled at a recent test day have helped sharpen his Falcon.

“It’s a good confidence builder,” he said of topping the session.

“The car felt pretty good, (but) I still think we need to work on a few little things with the car.

“It’s hard to get a full read on it at the moment, but it feels like it turns a bit better which is something we’ve been working on.

“The whole weekend is a big test for us to see if some of our new components work.”

Co-drivers Matt Campbell (#7 Nissan), Tony D’Alberto (#17 DJRTP Ford), Luke Youlden (#12 DJRTP Ford) and Cameron McConville (#222 LDM Holden) all cut laps in the session.

Karl Reindler also shared the Team 18 Holden with Lee Holdsworth, whose brief run followed his return to the cockpit during a shakedown at Winton on Monday.

“I felt quite comfortable but it was a bit hard because the car had no grip,” said Holdsworth as he works up to a race return at Sandown next month.

“I was going to ask Karl if he’d done burnouts on the way in!

“It was good to at least get back in and feel what the new car feels like again.

“I asked if I could have another set of tyres to get a bit more running but Karl was pretty keen to get back out there again.”

A second 60 minute session will complete the day’s Supercars track action.

Result: Virgin Australian Supercars Championship Red Rooster Sydney Super Sprint Practice 1