Bradley Perie took the spoils in the Sprint race as he narrowly beat Jamie van Sikkelerus by 0.069secs.
The Appleyard Macadam rider took his third win on the bounce and fifth of the season as he finished just ahead of the Dutchman, with Lee Johnston third.
Polesitter Tom Booth-Amos had to make do with fourth, just ahead of Luke Jones in fifth.
Harvey Claridge was the first GP2 rider home as Jack Scott crashed early on, with Mason Law second and Cameron Fraser third.
Quattro Group British Supersport & British GP2 Cup, Donington Park, Race One:
1. Bradley Perie (Appleyard Macadam Racing)
2. Jamie van Sikkelerus (MPM Routz Racing) +0.069s
3. Lee Johnston (Ashcourt Racing) +1.116s
4. Tom Booth-Amos (Gearlink Kawasaki) +4.113s
5. Luke Jones (Highsparks Ducati) +9.980s