With Broc Feeney (#88 Red Bull Ampol Camaro) second, Brown cut Kostecki’s championship lead to 87 points heading to the betr Darwin Triple Crown.
Kostecki held off Shane van Gisbergen (#97 Red Bull Ampol Camaro), who finished fourth after crashing out of Sunday’s first race.
Jack Le Brocq was fifth for Matt Stone Racing, with Chaz Mostert (#25 Mobil 1 Optus Mustang) and Cam Waters (#6 Monster Mustang) the first Fords home in sixth and seventh.
Brown left Kostecki for dead when the lights went out, and enjoyed a clear lead into Turn 2.
Waters, who started third, dropped to sixth behind Le Brocq, Feeney and Tim Slade (#23 Nulon Camaro).
Andre Heimgartner (#8 R&J Batteries Camaro) was forced to surf across the Turn 2 infield off the start, but safely rejoined without incident.
Kostecki haunted the rear of his teammate, but Brown slowly opened up a margin as Feeney demoted Le Brocq to fourth.
Down the pack, Heimgartner’s action-packed start continued when he tripped over James Courtney (#5 Snowy Rivers Caravans Mustang) into Turn 2 on lap 9. Both cars surfed through the gravel, but no further action was taken over the incident.
10 laps later, Courtney made contact with Heimgartner’s teammate Macauley Jones (#96 Pizza Hut Camaro) through the final corner, with Jones sliding across the front of the #5 Mustang.
Van Gisbergen, aboard his repaired #97 Red Bull Ampol Camaro, stopped from eighth on lap 11.
Le Brocq and Slade disputed fourth, and the two made side-to-side contact at Turn 6 on lap 16. It opened the door to Waters, and it became a three-car battle.
Cameron Hill (#35 Truck Assist Camaro) stopped from eighth on lap 20, having been passed for seventh by Mostert just prior to his stop.
Kostecki and Le Brocq stopped on the following lap, the former in an effort to pounce on teammate Brown, whose margin had opened up to 1.4s.
Le Brocq emerged just ahead of van Gisbergen, with the two Camaros making contact exiting the Turn 4 hairpin.
Brown stopped at the end of lap 23, and emerged with an extended 2.5s lead over his teammate.
Feeney, Waters and Mostert came in on lap 24 – when they emerged, the order ran Brown, Kostecki, Feeney, van Gisbergen, Le Brocq, Waters, Hill and Mostert.
Slade split Le Brocq and Waters to make it an effective Chevrolet top six, which became seven when Waters bowled a wide at the hairpin on lap 27.
Waters forcefully regained the position at Turn 6 on lap 29, with Mostert also clearing the #35 Truck Assist Camaro.
All the while, Kostecki dramatically fell away from Brown, with Feeney quickly catching the #99 Coca-Cola Camaro.
Feeney easily passed Kostecki at Turn 4 on lap 32; behind them, Mostert passed Waters, and Slade crawled to pit lane with a mechanical issue.
Van Gisbergen demoted Kostecki to fourth at Turn 6 on lap 35, with the series leader retaking the position at the same corner three laps later.
It meant little to Brown, who sailed to his second win of the season by 3.9922s over Feeney, with Kostecki 8.7320s from victory.
Mark Winterbottom (#18 DEWALT Camaro), Anton De Pasquale (#11 Shell V-Power Mustang) and Bryce Fullwood (#14 Middy’s Camaro) rounded out the top 10.
Hill came home 11th, with Slade five laps down in 25th and last.
Kostecki leads Brown by 87 points, with Mostert 166 points down in third. Van Gisbergen is fourth, 172 points down.
The 2023 Repco Supercars Championship will resume at the betr Darwin Triple Crown on June 16-18.