KMR Sport's Lucas Blakeley gained four spots on the first lap at Donington Park, to claim his third GB4 win of the season in the opening race of the weekend.
He finished five seconds clear of Elite's pole-sitter Finn Harrison, with Harrison's teammate Alisha Palmowski third.
Harrison led the field away from pole at the start, while championship leader Linus Granfors initially moved past Leon Wilson into second, only to slow dramatically on the run to Redgate and fell back through the field.
Blakeley meanwhile had already moved up into third, and dispatched Arden's front row starter Leon Wilson for second at Hollywood. The top two then built a gap, but Harrison encountered trouble at Melbourne and Blakeley was up from fifth to first at the end of the opening lap.
From there Blakeley was able to gradually pull away, taking his third win of the year by over five seconds from Harrison, while Palmowski was able to pass Wilson late on to secure third.
Despite falling back to 10th on the first lap, Granfors was able to minimise the championship damage, his cause aided when nearest rival Harry Burgoyne encountered trouble on the formation lap and had to pit, emerging a lap down.
Granfors' recovery moved him up to ninth on lap two, sixth on lap three and then was stuck in a Wilson, Palmowski and Callum Baxter train for several laps.
But when Wilson went wide at McLeans on lap nine, that triggered a chain reaction as Palmowski battled past, while the door opened for Granfors to pass both Baxter and Wilson before the Fogarty Esses.
While the top-two had broken away, all eyes focused on Palmowski and Granfors, with the Elite Motorsport contender staying ahead by half a second at the chequered flag.
Granfors therefore took fourth but minimised the damage in his championship fight, while Palmowski's podium ensured she moved into second place in the standings.
Behind that squabble, Baxter held fifth ahead of Wilson, with Fox Motorsport's Branden Templeton battling back from an early spin to take seventh, setting the fastest lap in the process.
Nickolas Ellis claimed eighth for Elite on his GB4 debut, ahead of Fortec's Jack Taylor and KMR's Chloe Grant.
GB4 Championship, partnered by the BRDC, Donington Park race one provisional result:
1. Lucas Blakeley, KMR Sport, 12 Laps
2. Finn Harrison, Elite Motorsport, +5.379s
3. Alisha Palmowski, Elite Motorsport, +11.954s
4. Linus Granfors, Fortec Motorsport, +12.542s
5. Callum Baxter, Graham Brunton Racing, +14.510s
6. Leon Wilson, Arden Motorsport, +15.021s
7. Branden Templeton, Fox Motorsport, +24.022s
8. Nickolas Ellis, Elite Motorsport, +25.151s
9. Jack Taylor, Fortec Motorsport, +30.657s
10. Chloe Grant, KMR Sport, +32.580s
11. Megan Bruce, Fox Motorsport, +34.083s
12. Aleksander Mizera, Idola Motorsport, +40.147s
13. Dan Hickey, Fortec Motorsport, +40.722s
14. Ava Dobson, VRD Racing, +44.780s
15. Harry Burgoyne, KMR Sport, +2 Laps
