After banking pole with a record-breaking lap, Herne made a perfect start to the first 17-lap race of the weekend.
The Garry Rogers Motorsport driver then staged a race-long battle with 2022 Australian Drivers' Champion Joey Mawson.
The pair traded fastest laps throughout the race, Herne doing enough to hold a 1.5-second lead over Mawson at the finish.
The win was the Trans Am regular's first in an S5000 car and gives him an early Tasman Series lead.
Jordan Boys finished third, more than 10 seconds back, ahead of Ben Bargwanna and S5000 debutant Noah Sands.
Fellow debutants Jude Bargwanna, Mark Rosser and Elly Morrow were next, while Cooper Webster was a DNS following his qualifying crash.
The S5000 action continues with races at 8am and 10:55am local time tomorrow.
