Sam Laffins celebrated his first win of the year at Donington Park as Aaron Silvester threw away the championship lead with a uncharacteristic crash three laps from home.
Laffins took the lead when Silvester tipped off on lap nine of 12, taking victory by 2.578secs over Owen Jenner, who has now jumped into the points lead.
Edmund Best secured the final podium position as he crossed the line just 0.225secs ahead of Finley Arscott while Cameron Dawson rounded out the top five.
Pirelli National Junior Superstock with Santander Consumer Finance, Race result:
1. Sam Laffins (G&S Racing)
2. Owen Jenner (Jenner Racing) +2.578s
3. Edmund Best (Symcirrus Motorsport) +3.092s
4. Finley Arscott (MIH Solutions Hand Racing) +3.317s
5. Cameron Dawson (MSS Performance) +3.719s
Championship positions after Round 13:
1. Owen Jenner 228
2. Aaron Silvester 213
3. Cameron Dawson 199
4. Asher Durham 191
5. Edmund Best 141