Ford Mustang GT drivers Cameron Waters and James Moffat finished second with rookie Brodie Kostecki and David Russell earning a podium despite the Erebus Motorsport team denied a shot at the Top 10 shootout earlier in the day for running underweight cars in qualifying.
"It was a pretty tough race, when we did that [puncture] I knew it was going to be a tough slog, but credit to the guys, this car has been speedy all weekend," Mostert said.
"We started on pole and we won the race and every time you start on pole you never think you're going win it, credit to this car and credit to the team.
"To all the fans; it's so good to have punters back at the track, I'm out of breath."
After 145 laps of jostling between van Gisbergen and Mostert it looked as if the Aussie had the edge after the final pit stop. Van Gisbergen entered from second a few laps after Mostert and came out more than five seconds behind only for another twist when Broc Feeney ended up in the sand and brought out the safety car one last time. That set up a sprint for the finish, but van Gisbergen and Waters had no answer for pole sitter Mostert.
Van Gisbergen and teammate Garth Tander ended up finishing 18th. Four-time winner Jamie Whincup in his final race as a fulltime driver finished in fourth.
It was a relatively drama-free race through the first 105 laps with Mostert, van Gisbergen and Waters sharing the front. Bathurst is used to a kangaroo stopping racing but a rogue echidna seemed to provide a first by strolling on the track at the Cutting and forcing a yellow flag with 56 laps to go.
That brought the pack back together with van Gisbergen leading the restart only to lose it again to Mostert after another stoppage and run into the pits. When Jake Kostecki hit the wall at turn 18 on lap 121 it brought another safety car. Once the race restarted that left 37 laps and one stop – practically a sprint race for the win. It was all on for 30 of those laps before van Gisbergen began to lose speed and it was evident his title hopes were over.
Once Mostert finished his celebrations with Holdsworth in pit lane, there was a special presentation for 2021 Supercars Champion van Gisbergen, his second series crown.
"Bittersweet," said van Gisbergen of the championship win celebrations.
"I really tried to win that race. Congrats to Chaz and Lee and their team. They were super fast. Gave it everything and just couldn't quite hold it together.
"It's been an awesome year, otherwise. I've got to thank all these legends, it's been a really, really good year otherwise. We'll drink a few out of this [trophy] tonight."