As was the case in the opener, the outside of the front row proved to be the place to be for the start.
It was from there Webster was able to jump pole starter Mawson to lead.
Across the two laps that followed he was able to pull a small gap as Mawson was left looking at third-placed James Golding in his mirrors.
On lap 3 Webster's early advantaged was erased when debutant Winston Smith buried his car on the outside of Southern Loop, prompting a safety car.
The lap 6 restart proved critical for Mawson, the two-time Gold Star winner sweeping past Webster and grab the lead.
Webster did try and hit back at turn 4, with Mawson able cover on the inside and retain the lead.
By that point the race had gone time certain with just three minutes remaining with Mawson looking primed for a fifth straight win for the season.
However, while it was Mawson who crossed the line first, he was promptly hit with a five-second penalty for a restart infringement which dropped him to fourth.
It also promoted Webster to victory, the first that hasn't gone to Mawson so far this season.
"The start I nailed today, I was back to where I should have been yesterday," said Webster. "And then I got a gap. It was a bit tricky because we're not used to the conditions today, it was a bit different, a bit slippery.
"I was happy with my driving at the beginning of the race and I was pulling away. And then the safety car came out, which made a bit more difficult. But Joey made a mistake and you just can't do these things.
"In the moment I thought I'd made a mistake on the restart, that I didn't nail it and he got me into turn 1. I was a bit furious about that.
"I wasn't aware of [the penalty] until I saw the black flag coming through. Then I knew I just had to hold off Jimmy [Golding] to secure the win."
Golding ended up second having held off a brief challenge from Garry Rogers Motorsport teammate Aaron Cameron at the restart.
Cameron was promoted to third thanks to Mawson's penalty, ahead of Mawson, Blake Purdie and Nic Carroll.
The round concludes with a final race at 3pm local time today.
