David Shoubridge beat Tom Tunstall to take his 10th victory of the year by just 0.182secs.
The pair stuck close together throughout the whole race as they gapped the rest of the pack and despite his best efforts Tunstall was unable to find a way past his rival and had to settle for second.
Blaze Baker took third, just ahead of Max Lofthouse as Michael Tustin rounded out the top five.
Ducati Performance TriOptions Cup, Oulton Park, Race One:
1. David Shoubridge (Rich Energy Ducati)
2. Tom Tunstall (Motorcycle Race Parts) +0.182s
3. Blaze Baker (Trackdemons Racing powered by HMY) +9.122s
4. Max Lofthouse (JDF Racing) +9.588s
5. Michael Tustin (AH Performance/Breckland Utility Solutions) +15.676s