The first of today's two races was defined by a wild first corner clash that left just five cars running.
The incident was triggered by Versa Motorsport teammates Webster and Blake Purdie coming together at turn 1 as they squabbled over second position.
Purdie out-braked himself and clattered into Webster, while behind them Winston Smith hit Jordan Boys.
Mark Rosser then got involved as he made contact with a limping Purdie on the exit of turn 2.
The clash left Webster, Purdie, Smith and Rosser all out of the race, while Boys had to pit for a new wing.
The DNF was particularly costly for title contender Webster, especially as Mawson was left clear to streak to a second victory of the weekend ahead of James Golding and Aaron Cameron.
The final race of the weekend was a significantly tamer affair, Mawson completing a clean sweep with a lights-to-flag win.
The two-time Gold Star winner was untroubled across the 17-lap distance, even setting a new lap record of 1m18.165s on the final lap.
"It was a mega weekend," said Mawson. "What can I say? Another clean sweep, championship lead extended... mega. I'm absolutely over the moon."
Golding finished second for a third time for the weekend ahead of Cameron, Webster and Boys.
The S5000 season continues at the Sydney SuperNight at the end of July.
