With a maiden tour victory on the line, Hillier slotted a four-foot birdie putt into the middle of the hole to claim victory.
"I'm over the moon, it definitely wasn't easy. Marcus, who came second, he put up a good fight the whole day, kept the pressure on me... just real stoked to get over the line," Hillier said.
He said an eagle to finish a tough opening round - an even-par 71 - was the moment that gave him the belief and focus he needed to lift his game and chase down the leaders.
"I was two-over through 17 holes in my first round and wasn't really in a great place. I was thinking about home a little too much, I wasn't playing great.
"I managed to finish that round up well... and probably had the round of my life in round three so it all just fell into place nicely."
The victory earned Hillier a purse of $52,000 and he jumped 27 places on the tour's order of merit to move to 18th overall. The top 20 automatically earn a spot on the top-tier European Tour next season.
"That's what I'm setting my sights on in two weeks' time. It's pretty easy to get excited for it when you know it's your last tournament and you just need to make the most of it, so it's going to be pretty exciting."
The final event of the Challenge Tour will take place in Mallorca from November 4.