"Some numpty went to start the car and pushed the fire extinguisher button, so she was a bit of a panic," van Gisbergen told speedcafe.com.
The "numpty" was van Gisbergen.
The car had to be cleaned and the extinguisher refilled, but van Gisbergen, the race favourite after success in both curtain-raiser races over the weekend, missed the cut-off time to clear pit lane and was forced to start the 28-lap race from there.
He set about picking off his 15 rivals one by one and with 10 laps to go took the lead.
Fellow Kiwi Supercars driver Andre Heimgartner was second and rookie Matthew Payne third.
Four-time Bathurst winner and 1994 Grand Prix victor Greg Murphy was 10th and Ken Smith, the oldest competitor at 79, finished in 15th place.