It was the third feature win at three tracks this season for Dahm who has also tasted success at Palmerston North and Kihikihi.
The only disappointment was not having a chance to duel with his brother who started alongside on the front row but fell back with a brake problem.
"I was just a bit gutted to not have a battle with Keaton," said Dahm.
A close battle for the podium saw Aucklander Dean Shadbolt holding off Tauranga's Colin Entwisle with Greg Pickerill (Hamilton) and Keaton Dahm completing the top-five.
Former national champion Sam Waddell (Tauranga) continues to set the pace in the Super Saloon cars. He won the opening heat race and the 20-lap feature which gives him an impressive scorecard of six wins from nine starts at his home track this summer.
Chris Cowling (Tauranga) was the second heat winner and chased Waddell for the first 12 laps of the feature until he was sidelined with a flat right front tyre. Waddell led home Steve Cowling and Scott Hayward.
The first 2021-22 season appearance by the Formula 2 Midget Cars saw Matamata racer Benjamin Mathews win both heat races but it was Cole Robertson (Auckland) who had the feature winning pace to lead home Mathews and Leyton Kendall (Auckland).
The third event of Baypark Speedway's "Summer Slam" holiday series is on Saturday night (January 8) with Super Saloons, Saloons, Stock Cars, Six Shooters and Youth Mini Stocks on the programme. Racing starts at 6.30pm.