Kostecki and co-driver David Russell were contenders throughout Sunday's Great Race, sitting second behind leaders Shane van Gisbergen and Garth Tander for the middle part of the race.
However a bizarre run-in with a recovery vehicle less than 20 laps from the finish proved costly for the Erebus pair.
Still sitting second, Kostecki had just served his final stop of the race when the race fell under caution thanks to Will Davison hitting the wall at Griffins Bend.
As Kostecki emerged from pit-lane he found himself behind a recovery vehicle which about to head up Mountain Straight to retrieve the Davison Mustang.
At the same time Chaz Mostert, who had been running third and had stopped a lap earlier, arrived on the scene and was looking to get to the control line before Kostecki.
With Kostecki forced to lift because of the road-going ute on the track, Mostert able to race past and cross the line ahead of Kostecki.
He was allowed to keep the position for the restart several laps later, Mostert going on to finish second while Kostecki ultimately slipped back to fourth behind Cam Waters.
Despite remonstrating angrily over the radio at the time, Kostecki kept his cool when speaking to media about the incident post-race.
He said he backed the safety first approach and labelled the situation a case of bad luck.
"Unfortunately we were a bit unlucky, so we got the wrong side of the timing," said Kostecki.
"There was a car stuck in the fence and safety comes first and unfortunately we got a bit of bad luck there.
"I thought I was in front of Chaz but it was really hard to see as he was in my blind spot. I definitely saw that he wasn't in front of me to the point where I lifted but that is not the line and I was trying to navigate the safety truck as well as him.
"I saw him coming last minute as well. I had to lift so we didn’t have monumental with the safety truck.
"It is a bit disappointing as it might have put us on the podium. I’m not really sure. But we didn’t have a fast enough car today [to win]. We will have to try again next year."
When asked if the recovery vehicle systems needs assessing, Kostecki added: "I’m not really sure to be honest. I mean I’m not sure where else you can park one of those safety trucks to get access to Turn 2 as there are walls all along [Mountain Straight].
"It is a bit of tricky one. The safety crew in Supercars always do an awesome job with that sort of thing. I think it is a one-off thing here. I don’t think it has ever happened before."
While he missed out on a Bathurst podium, Kostecki was buoyed by a promising day off speed amid a somewhat inconsistent season for Erebus.
"The car was mega and credit to the whole team, they didn’t make a single mistake the whole day," he said. "I have to make a big shout-out to David Russell as well who did an awesome job for the second year. He was able to hang onto Garth [Tander] and he did an awesome job.
"We really executed the day in terms of strategy with [engineer] George Commins. Unfortunately we didn’t have enough power to keep with the front guys."
