Ben Currie beat Luke Stapleford to FP1 bragging rights by just 0.165s as the action began at Donington Park.
The Oxford Products Racing Ducati rider clocked a 1min 31.712s lap to end the session on top, with Stapleford second.
Rhys Irwin was third quickest aboard the Astro-JJR Suzuki, with Tom Toparis fourth and Seth Crump fifth.
Joe Collier shot straight to the top of the GP2 order, the Kramer rider ending the session seventh overall, with Cameron Fraser second of the GP2 runners and Harry Rowlings third.
Quattro Group British Supersport and GP2 Championships, FP1:
1. Ben Currie (Oxford Products Racing Ducati) 1min 31.712s
2. Luke Stapleford (Profile Road & Racing Performance) +0.165s
3. Rhys Irwin (Astro-JJR Suzuki) +0.372s
4. Tom Toparis (Macadam Racing) +0.764s
5. Seth Crump (Seeeeeth) +0.978s