'Can't believe it': Supercars champ wins The Bend 500

Defending Supercars champion Chaz Mostert has triumphed in the first endurance race of the season, navigating wet and wild conditions to claim The Bend 500.

Mostert triumphed for Walkinshaw TWG Racing with co-driver Fabian Coulthard in a stop-start 147-lap race on Saturday that included three safety cars.

It was Mostert's second win of his title defence, last driving the new Toyota Supra to victory in May in Tasmania.

"I can't believe it. I can't f***king believe it," Mostert said over the race radio.

Last year's grand finalist Kai Allen and co-driver Tim Slade were second, ahead of Walkinshaw's all-New Zealand line-up Ryan Wood and Jaxon Evans in third.

Allen's Grove Racing teammate Matt Payne crossed the finish line in fourth but was demoted to sixth with a five-second penalty for colliding with rookie Jayden Ojeda in the final stages.

PremiAir Racing driver Ojeda took fifth place, behind Triple Eight's Will Brown.

Series leader Broc Feeney endured a horror outing with co-driver Nick Percat, finishing 24th out of 26 in the Triple Eight car.

Last year's race winners Brodie Kostecki and Todd Hazelwood were nowhere near the top, finishing 17th after starting from pole position.

Torrential rain had wreaked havoc from lap 25, with Rylan Gray's Dick Johnson Racing co-driver Tony D'Alberto bringing out the first yellow flag after spinning off track due to aquaplaning.

Race control kept the safety car out until the rain dispersed enough on lap 33, but a second stint due to extreme weather was required from lap 45.

The race restarted on lap 50, only for further rain to force a third yellow flag three laps later.

Conditions finally eased from lap 59, with Mostert doggedly working his way to the lead from 11.

Hazelwood had squandered Kostecki's hard-earned pole position and was swallowed by the front pack after failing to launch from lights out.