Englishman Justin Rose and Scottish pair Calum Hill and Ewen Ferguson were then in a tie for fourth on seven under, one ahead of Dane Niklas Nørgaard.
Starting the day three shots off the lead, Hillier came agonisingly close to holing his 22-foot eagle putt at the par-five third but instead had to settle for a tap-in birdie. The 24-year-old gave the shot back after finding water at the sixth, but did well to limit the damage to just a bogey.
He bounced back with a five-foot birdie on the ninth before parring each of the next five holes to remain some way off the pace, but that suddenly changed at the long 15th as Hillier drained his 40-foot eagle effort to jump to seven under par.
And he followed that up with a stunning fairway bunker shot on the 16th to set up a close-range birdie, which earned him a share of the lead. Hillier kept his foot on the gas at the par-five 17th, launching his second shot to six feet before tapping in the putt for his second eagle of the day.
Heading down the 18th with a two-shot lead, Hillier sent his second shot from the rough over the back of the enormous green – landing his ball alongside the trophy. Knowing he still had work to do to avoid running up a big number, the New Zealander played a well-judged third before saving par from eight feet to give the chasing pack no realistic chance of catching him.
Hillier, who also recorded recent top-five finishes at the KLM Open and BMW International Open, was thrilled to enter the winner’s circle.
He said: “I’m over the moon and a bit lost for words. Those last few holes are going to take a while to process I think.
“The 15th – that tee-shot’s been troubling me all week. It was nice to get one semi in play. A bit of an awkward lie for my second shot but managed to have a good five wood in there to 40 feet. The putt was racing but I managed to hit the back of the hole so that was a nice little bonus.
“And then a bit of a miscue on the 16th. Put it in that fairway trap but actually had a nice number in so it was a nice full wedge in there and I managed to get a nice little bounce off that slope. And then the 17th was a bit lucky. I just carried that trap and managed to make the most of that good break.
“Then just held on for dear life down the last. I felt pretty good over (the final putt). I felt as comfortable as you can over a putt of that magnitude. And I just had to tell myself to put a good stroke on it.”
Hillier follows in the footsteps of countryman Bob Charles, who won this event in 1972, and he was thrilled to be in such illustrious company.
He added: “That’s pretty amazing. Obviously he’s New Zealand’s golfing hero so it’s pretty cool to be on the same trophy as him.”
Earlier in the day, John Gough posted a closing round of one-over to end up at +1 for the tournament and tied for 39th. The English-born Irish Amateur Open champion, whose parents are both Irish, was the only amateur in the field and for two rounds had threatened to become the first amateur to win on the European Tour since Shane Lowry’s fairytale win at Baltray back in 2009.