It did not always look likely as Hillier got off to a slow start on the St Andrews layout. He opened with three bogeys in the first seven holes as he tried to close out his first age-grade national title.
But Hillier rallied with birdies on the 8th and 10th to restore his lead.
Meanwhile Mazey, who birdied the opening hole to get into a share of the lead, faded in his first nine holes to the final round as he made the turn in four-over par 41.
Concepcion had his chance to claim the title when he delivered a couple of late birdies but bogeys in three of the final four holes thwarted his challenge.
Hillier mixed a bogey and birdie on the 13th and 15th and then parred his way home to secure the title comfortably.
After rounds of 69, 75 and 73 for a one-over par total, Hillier was a deserved champion as he followed in the footsteps of the likes of Phil Tataurangi, Mark Brown and Brad Iles as North Island Under-19 champions.
"I got off to a slow start but it was pretty windy and conditions weren't easy. I birdied 8 and 10 and felt more relaxed. I played really well coming home and got the result," he said.
Hillier is a talented footballer, who trialled for West Ham as a 10-year-old, but playing golf in the US is his main goal.
"My main focus is playing three or four tournaments in June in front of the Oregan Golf coach and then he makes the decision on scholarships."
Meanwhile, in the women's division at the Ngaruawahia Golf Club, Auckland Jocelyn Katu sealed her first national age group title.
The Aviation Golf Club member carded a 10-over par 82 in the difficult conditions of the final round to win by two shots from Jiyeon Park (South Korea).
Alanna Campbell (Omanu) was the best of the Bay girls in sixth place on 230, with Tyla Kingi fading with an 89.
