As has been the case across the weekend so far, van Gisbergen looked to have a pace advantage on the field in the early stages of the 20-lap finale.
He barged his way past the likes of Cam Waters, Nick Percat and Mostert in the first five laps, before jumping Dick Johnson Racing pair Will Davison and Anton De Pasquale with his Lap 6 stop.
However Walkinshaw Andretti United's pit work was even slicker than Triple Eight's, Mostert taking his service on Lap 7 before resuming right in front of van Gisbergen.
Still, at that point it looked like van Gisbergen had Mostert's measure – until Lap 9 when he locked his front-left into Turn 9.
The resulting flat spot took the wind out of van Gisbergen's sails, Mostert able to charge into the distance and grab a second win for the weekend.
"We weren't that competitive on the soft at the start, but the boys did a fgamastic pitstop and we stuck to our strategy. That's what you've got to do, put Shane under pressure. He obviously had a beast under him, but one little mistake. The team did such an awesome job. They gave us the win in the lane today
Van Gisbergen did his best to nurse his flat spotted tyre to the end and got within a lap of an unlikely second place until it finally let go.
That forced him into another stop and left him 20th at the flag, although he was still able to secure the Larry Perkins Trophy for the most points across the weekend.
It also meant the rest of the podium was made up of the DJR cars, Davison finishing ahead of De Pasquale.
Cam Waters finished fourth on the road but was hit with a five second penalty for a pit infringement which dropped him to seventh.
That elevated Slade to fourth ahead of Brodie Kostecki and Percat.
Will Brown was next ahead of Broc Feeney on the road, however the Triple Eight rookie copped a five second penalty of his own for a pit infringement and was dumped down to 12th.
