Hill ran straight on and made contact with the concrete wall at Turn 3 with two minutes remaining in what was to have been an hour-long session for the Repco Supercars Championship field at Wanneroo Raceway.

The Matt Stone Racing driver was able to exit the damaged #4 Supaglass Camaro under his own power but the session did not restart given the red flag had been called with just 1:54s remaining.

That locked Walkinshaw Andretti United’s Mostert into top spot after he blazed to a 0:55.0930s on his second lap of the afternoon in the #25 Mobil 1 Optus Mustang.

Wanneroo was warm and sunny when pit exit opened at 14:20 local time and the field rolled out on their soft compound tyres, for which minimum pressure has been lowered to 15psi this weekend.

Team 18’s David Reynolds (#20 Tradie Beer Camaro) was quickest after the first flyers on a 0:56.0553s before Mostert blew everyone away with that 0:55.0930s next time around.

Mostert’s rookie team-mate Ryan Wood (#2 Mobil 1 Truck Assist Mustang) was still more than half a second away when he moved into second spot with a 0:55.6045s moments later, as was PremiAir Racing’s Tim Slade (#200 Nulon Camaro) when he set a 0:55.5997s on his third lap.

A red flag was called after almost six minutes when Tickford Racing’s Thomas Randle stopped on-track with a prop shaft failure in the #55 Castrol Mustang.

Pit exit reopened just over four minutes later, after which Hill moved into second place on a 0:55.5991s, still 0.5061s away from Mostert’s early effort.

Reynolds had an off at Turn 7 in the 23rd minute but was able to drive through the sand and save another red flag, although the session was developing into something of a lull.

Erebus Motorsport’s Jack Le Brocq (#9 Bic Camaro) made a move into second place with a 0:55.4257s with just over a quarter of an hour remaining.

MSR’s Nick Percat (#10 Bendix Camaro) then halved Mostert’s margin over the field to 0.1753s when he set a 0:55.2683s on his fifth run, before Randle reappeared on-track after repairs in the Tickford garage.

Brad Jones Racing’s Andre Heimgartner put the #8 R&J Batteries Camaro into third on a 0:55.4240s with 11 minutes to go, before the Blanchard Racing Team’s James Courtney (#7 Snowy River Caravans Mustang) usurped him with a 0:55.2709s in the final three minutes.

There was no time for any further advances when the Hill incident triggered the second and final red flag of the day.

The top five was thus Mostert, Percat, Courtney, Heimgartner, and Le Brocq, with Triple Eight Race Engineering’s Broc Feeney (#88 Red Bull Ampol Camaro) sixth on a 0:55.4692s.

Brodie Kostecki (#1 Erebus Camaro) ended up seventh, from Will Davison (#17 Shell V-Power Mustang), Hill, and Slade, while championship leader Will Brown (#87 Red Bull Ampol Camaro) was 18th on a 0:55.8062s which was 0.7132s off the pace, and Matt Payne (#19 Penrite Mustang) 21st.

Practice 2, a 20-minute session, starts tomorrow at 09:15 local time/11:15 AEST.

Results: Practice 1