The Tasman title went somewhat unexpectedly down to the wire after Herne's four race winning streak was broken yesterday by a brush with the wall and a gearbox issue.
He limped around to finish 11th but saw his healthy margin over Mawson reduced to a single point.
It also dropped him to the second row for the start of the winner-takes-all finale while Mawson started from pole position.
Mawson made a clean start to the 15-lapper, initially leading Cooper Webster and Herne.
It didn't take long for Herne to work his way into second, though, the Garry Rogers Motorsport driver sliding under Webster at Turn 9 on the opening lap.
He then tucked under Mawson's rear wing before making what proved to be a dramatic and decisive move for the lead on Lap 3.
Herne tried to pass Mawson on the way into Turn 9 but found the inside line suddenly covered by a late defensive move from the leader.
That led to contact that ruled Mawson out of the race and out of the hunt for the title.
A wounded Herne was able to continue, albeit slowly, limping around to 13th at the finish as he sealed the title.
The clash between the leaders left Webster leading the field behind the safety car as the mess was cleaned up.
But he didn't hang on to the lead for long after the Lap 8 restart, Aaron Cameron barging through to set up his sole victory of the Tasman Series campaign.
Webster finished second with Blake Purdie rounding out the podium.
Jordan Boys and Noah Sands were fourth and fifth while Giancarlo Fisichella's high-profile cameo ended with a sixth place.
Australian open-wheel stalwart Tim Macrow was seventh in what was his final race as a full-time driver.
