The DP World Tour star went five under through his last five holes on Saturday, capped with a spectacular birdie-two after hitting his tee shot to four feet on the 18th at Millbrook Resort.
Hillier signed for a seven-under 64 and a three-round total of 18 under.
Countryman Kerry Mountcastle (64) and Australian Curtis Luck (63) both bogeyed the final hole to share second spot at 17 under, with Lucas Herbert a shot further back after a spectacular 62.
With the group of four tied for fifth well back at 13 under, it's shaping as a four-man showdown on Sunday.
Since 2003, the only Kiwi to salute in the national Open was Michael Hendry in 2017 - and the newly-married Hillier would love to end that long drought.
"I don't know when we've had this many Kiwis up the top of the leaderboard but it's great to see," said the 27-year-old, who has already recorded two top-five finishes on the DP World Tour in 2026.
On another day of low scoring across the board, Hillier had only recorded two birdies in his first 13 holes, before going ballistic with a birdie-birdie-par-eagle-birdie finish.
"That was crazy," he said.
"Obviously I didn't have my best early on but it was just one of those days where I had to stay patient.
"I knew there were a couple of par fives I could take advantage of and then it was pretty cool to get that one on the last in front of that massive crowd."
Victory for former world No.1 amateur Luck would be life-changing, with the added carrot of a guaranteed start in the British Open at Royal Birkdale.
The only blemish on the 29-year-old's card came with a bogey-four on the final hole, a mistake he could only put down to adrenaline after firing his tee shot over the back of the green.
"I played great, super steady and I don't think I did anything wrong," said the West Australian.
"I executed all the shots I wanted to so there was never really any stress."
Herbert was contemplating an early end to his tournament on Thursday after starting with three straight bogeys in the wind and rain.
Now the LIV Golf star is right in the mix for a seventh professional win, having previously saluted three times on the DP World Tour and once on the PGA Tour.
His nine-under 62 was only one shot shy of the Championship Course record at Millbrook.
"I made a couple of long putts when I needed to and I guess I just didn't hit it in the wrong spots at the wrong time," said Herbert.
"I'll probably go and kick myself a bit about not birdieing the (par-5) 14th with a 4-iron in.
"But every person on the planet after every single round of golf they've ever played will tell you about the one that got away, so I'll take that."
South Korean Chan Choi tied the course record with a sizzling 10-under 61 to move to 12 under.
