KMR Sport's Alex O'Grady claimed a second GB4 Championship win of the season in the opening race of the weekend at Snetterton, after taking advantage of mid-race misfortune for chief title rival and pole sitter Fred Green.
Green had led the opening six laps from pole position, but slowed dramatically on the seventh tour, handing the lead to O'Grady. The Irishman took full advantage to lead the rest of the contest and open up a big gap at the top of the standings.
A combative opening lap from Pace Performance's Torrin Byrne was the foundations of his run to second place behind O'Grady, while Douglas Motorsport's Dayton Coulthard recovered from a challenging first few corners to complete the podium, his fifth of the year.
At the start of the race, Green made the most of his pole position to head the pack down to Riches, while O'Grady slotted into second.
Behind, there was rapid progress from Byrne, who climbed into fourth by passing Coulthard on the run to the first turn, before squeezing up the inside of the Scotsman's teammate Conor Grant for third on the run to Agostini.
As the field started lap two, with Green holding a half second lead to O'Grady, Grant's hold of fourth place came to and end as he ran off the road at Riches while battling with Coulthard, and dropped to the tail of the field as he pitted to remove vegetation from his car.
At the front, the lead battle began to compress with the top three covered by less than six tenths of a second on lap four, while Coulthard also looked on course to join the scrap, having dropped from third on the grid to fifth on lap one.
But with Green just beginning to stretch his advantage, and the lead up to three quarters of a second entering lap seven, he was visibly slow approaching Agostini and his challengers streamed past him. The Elite Motorsport car pitted at the end of the lap, and retired, with what was later found to be an incorrectly fitted gearshift actuator.
That handed O'Grady a golden opportunity, and he led the remaining four laps, building his gap over Byrne to almost 1.7 seconds at the flag. The victory for O'Grady is his first non-Oulton Park triumph in GB4 and has extended his pre-event championship lead of 25 points into 60, not far off two clear race wins.
Byrne took his second successive runner-up spot on the podium, as he edged closer to a breakthrough win, while Coulthard was just over a second further back as he secured another podium, and moved up to fourth in the standings as a result.
Despite a five place grid penalty carried over from Silverstone, Fortec's Thomas Ingram Hill, who qualified third but started eighth, stormed to fourth after a superb fightback drive. The Brit dispatched teammate Franciszek Cegielski early on and benefited from the dramas ahead to finish just a second away from the podium spots.
Cegielski went from ninth on the grid to fifth, and finished just two tenths of a second ahead of Elite's Emmilio Valentino Del Grosso.
Pace Performance's John O'Donnell converted his best qualifying performance into seventh place, his highest race finish yet in GB4, 1.2 seconds ahead of teammate Josh McLean.
Hillspeed duo Connor Willis and Enzo Hallman completed the top-10.
The second race of the weekend is due to start at 09.10 BST on Sunday morning, with O'Grady looking to extend his lead further from pole position.
GB4 Championship, partnered by the BRDC, Snetterton, race one result:
1. Alex O'Grady, KMR Sport, 11 laps
2. Torrin Byrne, Pace Performance, +1.687s
3. Dayton Coulthard, Douglas Motorsport, +2.867s
4. Thomas Ingram Hill, Fortec Motorsports, +3.851s
5. Franciszek Cegielski, Fortec Motorsports, +11.157s
6. Emmilio Valentino Del Grosso, Elite Motorsport, +11.351s
7. John O'Donnell, Pace Performance, +13.483s
8. Josh McLean, Pace Performance, +14.652s
9. Connor Willis, Hillspeed, +15.248s
10. Enzo Hallman, Hillspeed, +15.418s
11. Jordyn Martin, Fortec Motorsports, +16.827s
12. Archie Davies, Scorpio Motorsport, +17.465s
13. Lily-May Watkins, KMR Sport, +22.609s
14. Archie Bullard, Fox Motorsport, +23.288s
15. Matan Achituv, Elite Motorsport, +23.667s
16. Michael Koh, Arden Motorsport, +25.010s
17. Romuald Bocquet, Scorpio Motorsport, +26.455s
18. Jamie Leverton, Nitrous Competitions ADM Racing, +28.029s
19. Solenn Amrouche, Arden Motorsport, +30.147s
20. Demitri Nolan, Hillspeed, +34.681s
21. Jasser Iskander, Fox Motorsport, +35.025s
22. Enzo Rujugiro, Fox Motorsport, +38.902s
23. Faris Organji, Scorpio Motorsport, +39.219s
24. Caitlyn McDaniel, Nitrous Competitions ADM Racing, +45.488s
25. Holly Miall, KMR Sport, +45.889s
26. Conor Grant, Douglas Motorsport, +1:30.574s
DNF. Fred Green, Elite Motorsport, 6 laps