Front-row pair Anton De Pasquale and Hazelwood made contact at Turn 1, after De Pasquale locked the rears and was set to run wide as Hazelwood turned in from the outside line.
That dropped them well down the field, to 13th and 20th, when the safety car was called after Richard Muscat and Jake Kostecki ended up in the Turn 3 wall.
When racing resumed on lap five, Le Brocq led team-mates Fullwood and Shae Davies in an all-Nissan top three.
Right behind them, Macauley Jones moved down the inside of Garry Jacobson at Turn 1 on the restart, contact firing the reigning champion wide and down the order.
The Nissan lockout ended when Fullwood and Davies clashed at Turn 10 and the latter was forced wide while looking around the outside, while Davies later had a run-in with Kurt Kostecki at Turn 1.
In the same phase of the race, De Pasquale went around at the final corner, Will Brown went off at Turn 1 from fourth, and Jacobson spun Andrew Jones at Turn 11, just after passing team-mate Josh Kean in the final chicane.
But it was contact between Jack Smith and Adam Marjoram at Turn 9, which left the latter beached, that brought the safety car back out, with Smith and Jacobson earning drive-throughs for their indiscretions.
That all elevated Dumbrell to third from 11th and Hazelwood into the base of the top 10, ahead of a two-lap dash to the flag.
Le Brocq was untroubled and led Fullwood and Dumbrell home, while Kurt Kostecki picked up fourth place when Macauley Jones went around at Turn 9 while fighting Davies.
Jack Perkins raced from 21st on the grid to finish fifth, ahead of Kean, while Hazelwood followed Perkins through the order after his first-lap off and finished seventh.
Debutant Jordan Boys was eighth, with Nathan Morcom and Mason Barbera rounding out the top 10.
Of the drivers involved in incidents, Andrew Jones finished 13th, one spot ahead of Davies – who had five seconds added to his time by stewards – De Pasquale was 17th, Macauley Jones 19th and Jacobson 20th.