Whincup was unaware smoke was pouring from his front right tyre in the closing laps and continued to push, saying it felt fine in the cockpit, and eventually finished 0.246s behind van Gisbergen.
"Shane was quick," he said. "We have pretty much the exact same car, exact same setup. I gave it a crack. It was all good fun, didn't bend any panels."
Holden's James Courtney, making a return to the track where he suffered serious injuries in a freak pitlane accident last year, finished third and Mostert, who earlier in the day claimed his fourth pole position of the season, came in fourth.
Scott McLaughlin was fifth and remains fifth in the championship standings. Fellow Kiwi Fabian Coulthard was 10th and Andre Heimgartner 23rd.
It was a day to forget for defending champion Mark Winterbottom, who didn't feature at the front of the field all day and could finish only 11th.
Holden veteran Craig Lowndes was sixth and will be aiming for a higher finish tomorrow when he makes his 600th career race start in a 52-lap race from 2pm.
- AAP