Jack Kennedy celebrated a double win at Knockhill after a race-long battle with reigning champion Ben Currie.
The Honda Racing UK rider went toe-to-toe with his rival through the 22-lap Feature race as the rain continued to fall in Scotland.
From pole, Currie got a quick getaway to lead lap one but Kennedy slotted in right behind him, hitting the front on the third lap, only for Currie to steal it back moments later.
The swapping of positions continued until Kennedy finally found a way past towards the end of the race, eventually crossing the line 1.643secs clear of Currie.
Third went to Luke Stapleford, who finished 4.413secs clear of Alastair Seeley as Owen Jenner rounded out the top five, taking the GP2 class win, as Keo Walker took second.
In the Cup class, Adon Davie took yet another win, with Ben Tolliday second and Adam Brown third.
Quattro Group British Supersport and GP2/HEL Supersport Cup, Feature Race result:
1. Jack Kennedy (Honda Racing UK)
2. Ben Currie (Oxford Products Racing Ducati) +1.643s
3. Luke Stapleford (Macadam Triumph Racing) +6.957s
4. Alastair Seeley (Binch Pro Yamaha) +11.370s
5. Owen Jenner (Kramer Racing) +11.405s
Championship positions:
1. Jack Kennedy 162
2. Ben Currie 153
3. Luke Stapleford 134
4. Alastair Seeley 97
5. Harry Truelove 84