Kostecki had a margin of eight seconds over the now Kelly Grove Racing steerer after the 36 laps that comprised the final encounter of Event 2 of the Repco Supercars Championship, despite a penultimate lap off.
Reynolds was a high-profile defector from Erebus in the last off-season, his 10-year contract cut nine years short in seemingly acrimonious circumstances.
It was ironic then, that his first podium for KGR coincided with Kostecki's first at Championship level.
Asked in the post-race press conference what it was like to share the dais with Reynolds, the current Erebus driver quipped, “I'm sure Barry [Ryan, team CEO] will give me a big bar tab because of that.”
Reynolds, who did not seem especially fazed, responded, “I don't know what to say to that… Don't you get a big bar tab anyway?”
Kostecki was also queried about the dynamic between he and Jamie Whincup.
The 23-year-old lured Whincup into a race-ending crash in last year's Bathurst 1000 and passed the seven-time champion with little difficulty in his early rise from seventh on the grid to second in a wet Race 5 of 2021.
Kostecki, however, dismissed the focus on his possible edge over one of the all-time greats as media hype.
“I don't think about that rubbish, to be honest,” he declared.
“That's all spooled up by you guys [media], really.
“Not to be rude, but I just go out and go race, so that's that only stuff I worry about.”
Whincup's (full-time) driving career now has an end date, that being the 2021 season finale, as part of his transition to the team principal role at Triple Eight Race Engineering.
Kostecki's name has been floated as a possible replacement, and about whether or not he had his hand up for the seat, he replied, “Nah, I've got both hands down; I let other people do that stuff.”
The West Australian native also spoke glowingly of the environment at Erebus, which he officially became part of when signed as Anton De Pasquale's co-driver for last year's Great Race.
“I absolutely love Erebus and Betty and Daniel [Klimenko, owners] have such a good family environment there,” he explained.
“We've really enjoyed ourselves this year but now we've had a taste of champagne, I think we need to push hard throughout the rest of the year and try and have some more of it.”
One of Kostecki's key relationships in Erebus is that which he has with engineer George Commins, who went the opposite way to Reynolds in moving from Kelly Racing at the end of 2020.
The other is with fellow rookie Will Brown, who steers the #9 ZB Commodore.
“George and I get along really good and I made him cry after the race, so I've got one up on him at the moment,” recounted Kostecki.
“I think he's really excited to go racing again and obviously he worked with Rick [Kelly] for a while.
“I think I'm just excited to go racing, every time I get in the car, and I always want to do well, so we're trying to push each other as much as possible.”
On working together with Brown, he added, “It's the only way to go about it, both being rookies.
“He's going to do things better than I can and I'll do things better than he can, so we can try to combine the two together, and hopefully it helps with the greater good.”
His and Kostecki's performances were a far cry from their experience of the day prior, when they were plagued by a multitude of technical problems.
The latter always thought podiums possible in his rookie season, but perhaps not at Sandown given how the weekend had begun.
“I definitely thought so,” said Kostecki of top threes in 2021.
“It's one of those things; if you don't think you have a chance, you shouldn't be here.
“If you'd asked me that question at the start of the weekend, after P1, I probably would have said ‘no', but it shows how strong Erebus is at the moment.
“We made a lot of changes before that race and I got pretty excited when I started picking a few off and when I saw Shane, I knew that he'd just be managing the gap, so I pushed as hard as I could and came up short.”
Kostecki is now 10th in the championship while Brown sits 15th, ahead of the Beaurepaires Tasmania SuperSprint at Symmons Plains on April 10-11.