Zak O’Sullivan took the Race 1 spoils in the GB3 Championship‘s second visit to Donington Park this season, in a race which saw the Carlin driver officially crowned as champion.
O’Sullivan started on pole, with the Hitech GP cars of Bart Horsten and Reece Ushijima in second and third.
The then-championship leader led from Ushijima and Roman Bilinski, with Ayrton Simmons, Christian Mansell, Sebastian Alvarez and Roberto Faria involved in an incident at McLeans.
Mansell hit Alvarez, before being collected by Simmons, with Faria going through the gravel trying to avoid the stricken cars.
The two Douglas Motorsport cars were in strife at the Melbourne Hairpin, as Tommy Smith collided with Reema Juffali, apparently owing to a gearbox issue.
The Australian would retire in the pits in during the safety car period.
The race resumed on Lap 4, with everyone staying relatively well-behaved from the restart.
Horsten began his recovery from a pitstop on Lap 5, moving back up to 17th place around the outside of Craner Curves, which became the inside of the Old Hairpin.
O’Sullivan led at the halfway stage, from fastest lap-holder Ushijima, Bilinski and Branden Oxley.
Ushijima began to close the gap in the closing stages, improving on his own fastest lap to put he pressure on O’Sullivan who still led with four laps to go.
Horsten had to make another stop to rectify a wheel issue, and set the fastest lap on the penultimate lap.
O’Sullivan took the win and the title, from Ushijima and Bilinski who completed the podium.
2021 Donington Park Race 1 Results:
| Pos. | No. | Name | Nat. | Team | Laps/Gap |
| 1 | 51 | Zak O’Sullivan | GBR | Carlin | 12 laps |
| 2 | 13 | Reece Ushijima | JPN | Hitech GP | +0.961s |
| 3 | 4 | Roman Bilinski | POL | Arden Motorsport | +6.733s |
| 4 | 68 | Branden Oxley | GBR | Chris Dittmann Racing | +7.222s |
| 5 | 34 | Tom Lebbon | GBR | Elite Motorsport | +7.991s |
| 6 | 23 | Bryce Aron | USA | Carlin | +9.215s |
| 7 | 3 | Javier Sagrera | SPA | Elite Motorsport | +9.696s |
| 8 | 78 | Frederick Lubin | GBR | Arden Motorsport | +13.089s |
| 9 | 90 | Alex Fores | GBR | Chris Dittmann Racing | +13.834s |
| 10 | 67 | James Hedley | GBR | Elite Motorsport | +14.503s |
| 11 | 18 | Ayrton Simmons | GBR | Chris Dittmann Racing | +14.776s |
| 12 | 7 | Roberto Faria | BRA | Fortec Motorsport | +15.528s |
| 13 | 21 | Christian Mansell | AUS | Carlin | +17.236s |
| 14 | 43 | Mikkel Grundtvig | DEN | Fortec Motorsport | +17.888s |
| 15 | 5 | Johnathan Browne | ROI | Hillspeed | +20.214s |
| 16 | 16 | Eduardo Coseteng | FIL | Fortec Motorsport | +21.783s |
| 17 | 33 | Flynn Jackes | AUS | Hillspeed | +22.267s |
| 18 | 50 | Bart Horsten | AUS | Hitech GP | +38.529s |
| 19 | 55 | Tommy Smith | AUS | Douglas Motorsport | DNF |
| 20 | 10 | Reema Juffali | SAU | Douglas Motorsport | DNF |
| 21 | 12 | Sebastian Alvarez | MEX | Hitech GP | DNF |
