Luke Stapleford emerged victorious after a three-way battle to take the Feature race win, eventually beating Richard Cooper by just 0.179secs.
The Profile Road & Racing Performance rider held off a charging Cooper over the line, as Ben Currie finished third, just 0.205secs adrift.
Cooper took the lead at the start but soon dropped behind Tom Booth-Amos who led for a handful of laps before Currie hit the front.
But Stapleford was close behind and a lap later moved ahead and despite a late push from Cooper, was able to hold it to the flag.Booth-Amos had to settle for fourth, ahead of Rhys Irwin.
In GP2, Joe Collier took the win aboard the Kramer, with Cameron Fraser second and Harry Rowlings third.
Quattro Group British Supersport & British GP2 Championships, Feature race result:
1. Luke Stapleford (Profile Road & Racing Performance)
2. Richard Cooper (Russell Racing) +0.179s
3. Ben Currie (Oxford Products Racing Ducati) +0.384s
4. Tom Booth-Amos (Gearlink Kawasaki) +2.494s
5. Rhys Irwin (Astro-JJR Suzuki) +2.834s
Championship positions after Round 4
1. Lee Johnston 64
2. Tom Booth-Amos 63
3. Ben Currie 62
4. Rhys Irwin 54
5. Luke Stapleford 47