"In the circumstances, yeah. I start a bit slowly, managed to get a few putts to drop halfway through, and kept trucking from there."
Three birdies trumped two bogeys on his opening nine before an eagle on the 460m par-5 10th provided momentum.
A bogey on the 11th was swamped by birdies at 12, 13, 16, 17 and 18.
Hillier sits six shots adrift of outright leader Terry Pilkadaris who is 23-under par.
The Australian finished nine-under par for the day as he chases his first title in 13 years.
The record aggregate at the national open is the 26-under par set by late countryman Kel Nagle in 1964 at Christchurch.
Another Australian, Nick Flanagan, performed well early after securing a hole-in-one on the 127m par-3 second.
He backed that up with birdies on the sixth, seventh, 10th and 15th holes to be six-under par for the day, and 13-under for the tournament.
Flanagan paid tribute to still and fine weather for his low-scoring.
"It like playing in a dome; the weather's perfect and the scoring shows that.
"Anything around six or seven-under is going to move you up [the leaderboard] but nothing crazy because there are too many good players and the course is playing too well."
The ace was the fifth of his career, but the first at a professional tournament.
"It was a straight forward shot - a wedge down the hill. The ball has been getting to that green quick over the last couple of days.
"I took a bit off the wedge, landed it a foot past the hole and it spun back.
"One of the boys called it two to three seconds beforehand."
