Franco Bourne took a commanding win of more than four seconds over Max Cook to celebrate his second victory of the season.
Cook, who dropped down to fourth after hitting a false neutral during the race, fought his way back up to second as Louis Valleley was third.
The fourth rider home was Seth Crump as Aaron Silvester crossed the line fifth.
Pirelli National Junior Superstock Championship, Knockhill, race one result:
1. Franco Bourne (Marvel HCL Motorsport)
2. Max Cook (Uggly & Co by Binch Pro) +4.587sec
3. Louis Valleley (Team Val-Tech Racing/Mortimer Racing +6.774sec
4. Seth Crump (Seeeeeth) +10.244secs
5. Aaron Silvester (A&J Racing) +11.179secs