The victory helped Kostecki to leapfrog team-mate Will Brown at the top of the standings by 23 points, although Brown did finish third thanks to penalties for Cam Waters and Shane van Gisbergen.
The big loser at the start was Andre Heimgartner, who squandered the pole position he'd earned earlier in the day with a slow getaway.
He was swiftly swallowed up by Kostecki, Brown, Waters, Cam Hill and Jack Le Brocq before James Golding snuck by to drop Heimgartner to seventh within two laps.
Out front Kostecki led the way from Brown, the Erebus pair settling into a rhythm separated by a little over half a second. As the first stint wore on that gap blew out, Kostecki pulling four seconds clear before Brown pitted on lap 17.
Waters followed Brown into the pits, using a slightly shorter fill to jump the second-placed car. Kostecki made his first stop two laps later, resuming in the effective lead ahead of Waters and Brown.
Again Kostecki was able to stretch his lead, now over Waters, to around four seconds in the second stint. That was until David Reynolds ended up off the road and out of the race on lap 33, resulting in the sole safety car of the evening.
Waters had just pitted in that moment, Brown and Kostecki following suit on the next two laps as the field settled behind the safety car. They did so still in that order, Kostecki in the lead ahead of Waters and Brown.
With the Reynolds Mustang retrieved, the race went green again with 11 laps to go, Kostecki making a swift restart to lead the field. But within a few laps there was bad news for Waters, who was slapped with a five-second penalty for an unsafe release from his pit box that required Broc Feeney to brake to avoid contact.
Bad news for Waters was good news from Kostecki, who was left with a car between himself and those he was left racing. That allowed him to cruise to the finish, his winning margin seven seconds.
"That's unreal, I can't believe how fast the car was," he said. "There's still a few things to work on, but unreal night. The thing was just a rocket ship."
Behind Kostecki it was a wild finish as Waters desperately battled for second on the road, despite his penalty. His aggressive defence from Brown brought Chaz Mostert and van Gisbergen into the game, creating a four-way battle for second.
Mostert used the bottleneck to great effect, jumping the lot and grabbing second place. Waters finished third on the road but was demoted to fifth by the penalty.
Brown and van Gisbergen staged a thrilling battle for what would become third, the Kiwi getting the upper hand after making minor contact to get past on the final lap.
However he too was slapped with a five-second post-race penalty for the contact that dropped him to seventh and promoted Brown back to the podium.
Le Brocq finished the race fourth from Waters and Tim Slade, with van Gisbergen, Bryce Fullwood, Mark Winterbottom and Scott Pye rounding out the top 10.
The Sydney SuperNight continues with a second 140-kilometre race tomorrow.
