Early spins from John Bowe and Neil Crompton sent both tumbling down the pack.
In a battle with Mark Skaife, Glenn Seton spun in turn two, causing him to beach on the inside curb, taking him out of the race.
Brock leaped off the line to an early lead, with Skaife and Perkins in hot pursuit.
Down the pack, Seton was struggling to regain lost track position and spun again on turn two.
Alan Jones began to pressure Skaife for second before eventually passing him in his pursuit of Brock.