Mikey Hardie took victory by just 0.052secs over Charlie Atkins, as James McManus took the title.
Jack Roach finished third, with Gus Rodio fourth and Joe Ellis fifth as McManus crossed the line seventh to claim the crown.
“It’s been an amazing season from start to finish, I just can’t thank the team and sponsors enough,” he said.
“It’s amazing and I can’t describe how happy I am. It’s hard to celebrate with Chrissy passing away and my thoughts are with the Rouse family and the Steeman family too.”
HEL Performance British Junior Supersport Championship with Motocourse, Brand Hatch, Race One:
1. Mikey Hardie (Completely Motorbikes/Affinity)
2. Charlie Atkins (Symcirrus Motorsport) +0.052s
3. Jack Roach (Completely Motorbikes/Affinity) +2.111s
4. Gus Rodio (Luxestar VIP/Symcirrus) +4.314s
5. Joe Ellis (JPR) +6.762s