Mikey Hardie got the better of Charlie Atkins to take the opening Junior Supersport win by 0.207secs as James McManus finished third.
Behind, Kieran Kent – who had been quickest in earlier practice – crossed the line fourth some five seconds behind, just ahead of Jack Roach.
HEL Performance British Junior Supersport Championship with Motocourse, Donington Park, Race One:
1. Mike Hardie, Completely Motorbikes/Affinity
2. Charlie Atkins, Symcirus Motorsport +0.207s
3. James McManus, Completely Motorbikes/Affinity +1.100s
4. Kieran Kent, D&P Lovell Kent Racing +6.497
5. Jack Roach, Completely Motorbikes/Affinity +6.531s