Mikkel Grundtvig won the final race of the weekend at Oulton Park for Fortec Motorsport, his third GB3 Championship win.
The Dane started on pole, ahead of Tommy Smith and Nick Gilkes.
Grundtvig made a storming start, while Smith struggled slightly more off the line but managed to hold the Gilkes behind in the Hillspeed.
Marcos Flack was squeezed onto the grass on the exit of Shell Oils, the Australian dropping to the back of the order at the end of the first lap.
Cian Shields slipped back a couple of positions, having retired from Race 2 earlier in the day.
Smith started to go with Grundtvig, the pair slowly starting to pull away from Gilkes who had himself built a slight gap to David Morales (Arden Motorsport).
Zak Taylor bounced off the kerb at Britten’s, allowing Branden Oxley an opportunity but he was squeezed onto the grass over the top of the hill, putting him at the mercy of Shields in the Hitech GP car behind.
Grundtvig began to break away after three laps, after Tommy Smith sat almost three seconds behind and at risk of attack from Gilkes.
Roberto Faria and Luke Browning were making moves back up the field having started at the back, but Matthew Rees and several others moved up several places when Browning stopped at Hislop’s after contact with Tom Lebbon on the entry.
Race 2 third-place finisher Joel Granfors profited from Lebbon running on at the chicane amid that collision, while Taylor and Oxley continued to squabble over fifth into Old Hall on Lap 7.
Granfors was in no mood to sit back in the reverse-grid affair, setting the fastest lap, while Morales displaced Gilkes to go third on Lap 10.
From Zak Taylor to Granfors, ten cars ran line astern, as the GB3 Championship’s reverse-grid race seemed to allay concerns the increased dirty air produced by the Tatuus MSV-022 would make it harder to follow.
Marcos Flack seemed to struggle for pace after the first-lap incident, and began to slip away from the rest of the field, while McKenzy Cresswell ran across the grass after contact with Javier Sagrera.
Alex Connor also ran off-track, those incidents serving to spread the midfield a little as the race entered its final three laps.
David Morales looked to be closing on Smith’s Douglas Motorsport car, but wasn’t close enough to chance a move on the final lap.
Mikkel Grundtvig took his third GB3 win from Tommy Smith, with Morales, Gilkes, Oxley, Taylor, Shields, Max Esterson, Sagrera and John Bennett rounding out the top ten.
GB3 Oulton Park Race 3 Results:
| Pos. | No. | Name | Nat. | Team | Laps/Gap |
| 1 | 43 | Mikkel Grundtvig | DEN | Fortec Motorsport | 14 laps |
| 2 | 16 | Tommy Smith | AUS | Douglas Motorsport | +5.841s |
| 3 | 77 | David Morales | USA | Arden Motorsport | +6.203s |
| 4 | 64 | Nick Gilkes | CAN | Hillspeed | +7.743s |
| 5 | 68 | Branden Oxley | GBR | Chris Dittmann Racing | +8.490s |
| 6 | 21 | Zak Taylor | GBR | Fortec Motorsport | +11.796s |
| 7 | 6 | Cian Shields | GBR | Hitech GP | +12.974s |
| 8 | 42 | Max Esterson | USA | Douglas Motorsport | +14.221s |
| 9 | 31 | Javier Sagrera | SPA | Carlin | +14.429s |
| 10 | 27 | John Bennett | GBR | Elite Motorsport | +16.817s |
| 11 | 8 | McKenzy Cresswell | GBR | Chris Dittmann Racing | +17.276s |
| 12 | 67 | James Hedley | GBR | Elite Motorsport | +17.661s |
| 13 | 35 | Callum Voisin | GBR | Carlin | +17.990s |
| 14 | 7 | Roberto Faria | BRA | Carlin | +18.188s |
| 15 | 50 | Joel Granfors | SWE | Fortec Motorsport | +18.647s |
| 16 | 34 | Tom Lebbon | GBR | Elite Motorsport | +19.091s |
| 17 | 53 | Matthew Rees | GBR | JHR Developments | +19.652s |
| 18 | 4 | Bryce Aron | USA | Hitech GP | +20.052s |
| 19 | 32 | Alex Connor | GBR | Arden Motorsport | +20.427s |
| 20 | 11 | Marcos Flack | AUS | Douglas Motorsport | +26.085s |
| 21 | 5 | Luke Browning | GBR | Hitech GP | DNF (damage) |