James McManus moved a step closer to the title as he beat Calum Beach to the second race win by 3.138secs.
Jack Roach finished a close third, and just 0.156secs behind Beach as Kieran Smith led his twin brother Christian home in fourth and fifth places respectively.
McManus is now 35 points clear of Kieran Kent with two races to go at Brands Hatch.
HEL Performance British Junior Supersport Championship with Motocourse, Donington Park, Race Two:
1. James McManus (Completely Motorbikes/Affinity)
2. Calum Beach (UPVC Outlet Racing) +3.138s
3. Jack Roach (Completely Motorbikes/Affinity) +3.294s
4. Kieran Smith (Smith Twins Racing) +3.363s
5. Christian Smith (Smith Twins Racing) +16.162secs