Glenn Irwin has fought through tricky conditions to clinch his first BSB race victory, while team-mate Shane Byrne crashes on the final lap but still secures his Showdown spot.
After a heavy rain shower soaked the Silverstone circuit in between qualifying and the race half of the track remained soaking wet while the rest dried out causing a headache for tyre selection and set-up options.
While some riders wanted the start delayed in order to give the track time to dry out, the race went ahead as planned with Jake Dixon taking the biggest gamble to lead into turn one – as fellow Showdown contender Peter Hickman started from the pit lane in order to switch to wet tyres.
As the BSB riders tested the levels of grip and pace Brookes stormed into the lead while bringing Hopkins and Irwin with him in a breakaway.
On lap five the BSB Showdown picture changed once more with Haslam falling at the entry to Vale while at the same time Irwin climbed past Hopkins and Brookes and into lead.
At the midway stage James Ellison saw his top six hopes effectively ended due to a technical issue with his McAMS Yamaha, but up front Irwin built a slender lead on Brookes and Hopkins. Despite his inexperience at the sharp end Irwin measured his pace to record an emotional maiden win.
It was a bittersweet final lap for the Be Wiser Ducati squad despite Irwin’s win as Byrne tumbled off from sixth place but due to results around him he holds a 50-point advantage over seventh-place Dixon meaning mathematically he will claim a BSB Showdown spot.
With Brookes clinching second place he has taken a huge step towards a top six title fighter spot, while Halsam requires just a handful of points in Sunday's two races to book his spot in the BSB Showdown.
Hickman battled back from his pitlane start to finish ninth for Smiths Racing BMW to keep hold of third place in the BSB standings.
Pole-sitter Jason O’Halloran slips to fifth after finishing 11th for Honda but still holds a useful points gap over Mossey in sixth, who claimed fifth place in the race, and Dixon in seventh who finished fourth in the Silverstone opener.
Christian Iddon also kept in contention for Tyco BMW with sixth place ahead of Taylor Mackenzie who claimed his best BSB result in seventh for Bennetts Suzuki ahead of Jakub Smrz on the Lloyd & Jones/PR Racing BMW with Hickman ninth.
BSB Silverstone race one results:
1. Glenn Irwin GBR Be Wiser Ducati Panigale R 33m 07.108s
2. Josh Brookes AUS Anvil Hire TAG Yamaha YZF-R1 +3.434s
3. John Hopkins USA Moto Rapido Ducati Panigale R +5.605s
4. Jake Dixon GBR RAF Reserves Kawasaki ZX-10RR +15.936s
5. Luke Mossey GBR JG Speedfit Kawasaki ZX-10RR +16.112s
6. Christian Iddon GBR Tyco BMW S1000RR +30.044s
7. Taylor Mackenzie GBR Bennetts Suzuki GSX-R1000 +53.685s
8. Jakub Smrz CZE Lloyd & Jones/PR Racing BMW S1000RR +56.728s
9. Peter Hickman GBR Smiths Racing BMW S1000RR +57.959s
10. Bradley Ray GBR Buildbase Suzuki GSX-R1000 +1m 00.610s
11. Jason O’Halloran AUS Honda Racing CBR1000RR +1m 08.452s
12. Lee Jackson GBR Smiths Racing BMW S1000RR +1m 11.688s
13. Sylvain Guintoli FRA Bennetts Suzuki GSX-R1000 +1m 22.061s
14. James Westmoreland GBR Gearlink Kawasaki ZX-10RR +1m 36.798s
15. Martin Jessopp GBR Ridersmotorcycles BMW S1000RR +1m 36.913s
16. Dan Linfoot GBR Honda Racing CBR1000RR +1m 37.868s
17. Michael Laverty GBR McAMS Yamaha YZF-R1 +1m 44.330s
18. Aaron Zanotti GBR Platform Hire Yamaha YZF-R1 +2m 17.897s
19. Luke Stapleford AUS Quattro Plant FS-3 Kawasaki ZX-10RR +2m 20.543s
20. Shane Byrne GBR Be Wiser Ducati Panigale R +1 lap
21. Shaun Winfield GBR Anvil Hire TAG Yamaha YZF-R1 +1 lap
Did not finish
Dean Harrison GBR Silicone Engineering Racing Kawasaki ZX-10RR
Andrew Reid GBR Tyco BMW S1000RR
James Ellison GBR McAMS Yamaha YZF-R1
Leon Haslam GBR JG Speedfit Kawasaki ZX-10RR
Tommy Bridewell GBR Team WD-40 Kawasaki ZX-10RR