Somehow, after a horror weekend, he had nabbed the lead of the race - though in the closing stages, that lead was increasingly threatened by eventual winner Chaz Mostert as the Red Bull crew screamed down the radio for the #1 racer to conserve fuel.
Whincup wrote he was happy to "clear the confusion" around whether or not he had radio, sayingit was clear, and that he understood the need to stick to a fuel number.
"At this point I was negotiating the most important 6 laps of my life on a tricky track full of sun glare and debris, and on worn tyres with no cool suit," Whincup wrote.
"I bent the rear view mirror away and had my head down doing what I do, I was fully aware of my fuel number and while I didn't hit that number every lap I had a clear calculation on the average and was absolutely on target to achieve that number before the chequered flag.
"The thing was that the game changed when we hit the reserve fuel tank, we know it's capacity is 2.5 laps but we had 3 to go.
"It was clear then that we were in a bit of trouble and the numbers we were working to weren't correct."
Whincup completely stood by his decision to power on in those final stages.
"In hindsight ... actually looking back only gives you a sore neck, we rolled the dice, gave it everything we had and ended up 5th.
"I'm sure the 12 other stories from our opposition are all a bit different, but this is our story on why we didn't win the great race."
For Whincup, it wasn't just the closing laps that made an impression on him. The difficulty of the weekend from the get-go- which he believed was the toughest he's had since joining the team in 2006 - with a bent tail shaft from Sandown in practice one, a "sick" engine replaced Thursday night, qualifying crash, and poor car balance all contributed, before the Great Race had even started.
A mistake at The Chase, ultimately costing Whincup a drive-through penalty could've been the end - but he would not say die.
"There was talk at this stage to circulate and save tyres for the next round but in my mind this wasn't even an option," he wrote.
"We were there to race and race hard and that's exactly what we did."
Despite the result, Whincup was still positive about what the team had achieved across the four days at Mount Panorama.
"To not only get our lap back but to lead the race on the last lap makes me so proud of my team, I can hardly explain the pride. Throughout the entire week it seemed that the more curve balls that came our way the more it lifted the crew and the harder they worked and fought for the prize - which to me means absolutely everything."