Herne kicked off Sunday's action with a lights-to-flag win in the first of two races.
The Garry Rogers Motorsport driver and Race 1 winner broke away from rival Joey Mawson early in the race, his lead as much as three seconds at points of the 17-lap race.
In the end a controlled effort yielded a 1.7-second winning margin.
Ben Bargwanna ended up third after Jordan Boys, who was a comfortable third in yesterday's opener, ended up down an escape road and dropped back to seventh.
The big mover was Cooper Webster, who started at the back of the grid after missing yesterday's race due to a qualifying crash. He managed to work his way up to fourth ahead of Noah Sands and Jude Bargwanna.
There was controversy early in the final race of the weekend thanks to a fast-starting Mawson.
The two-time Gold Star winner got alongside Herne heading into the first chicane, but was then forced to cut the corner once there wasn't room for the pair to run side-by-side.
That left Mawson with the lead, however he was instructed by race control to hand it back to Herne on Lap 3.
The two leading cars then continued their tense weekend-long battle, Herne able to just keep Mawson at arm's length.
There was one scary moment for the leader when he got loose in the beach chicane, but Herne was able to recover, re-focus and secure a clean sweep.
Boys ended up third after getting by Ben Bargwanna during the race, while Sands and Webster staged an exciting battle for fifth place.
S5000 rookie Sands did well to get by Webster on Lap 5, capitalising on a mistake from Webster in the beach chicane to grab fifth at Turn 11.
Webster then fought back late in the race, sneaking back into fifth at Turn 12 with three laps to go.
The second and final round of the Tasman Series will take place on the streets of Adelaide on the first weekend of December.
