The Excelr8 Motorsport Hyundai i30 N benefited from being one of those to pit at the end of the green-flag lap for wet-weather Goodyear tyres when rain made the going slippery.
Chilton was able to defeat Adam Morgan – the West Surrey Racing BMW 330e M Sport newcomer was another to pit at the same time – by 7.394 seconds as the rain increased, making it impossible for those on slick rubber.
The race began with first-race winner Dan Cammish keeping Tom Ingram at bay for the lead, but when Ricky Collard parked his Toyota on the track at McLeans with suspension damage that triggered the safety car, it gave those on grooved tyres even more of an advantage as they were able to close the gap to the stricken slicks runners in front.
Once the field was released again it took little time for Chilton and then Morgan to carve their ways to the front, and it was just a matter of time before those who had started on slicks eventually gave up the struggle and pitted.
As the race settled down, Chilton was leading Morgan and Scottish BTCC debutant Ronan Pearson, who had also pitted his Excelr8 Hyundai at the end of the green-flag lap.
In fourth spot was Nic Hamilton, with his brother Lewis watching on from the pit garage and with rain tyres he’d had fitted to his Team Hard Cupra Leon before the green-flag lap even began.
Hamilton soon fell victim to the Motorbase Ford of Sam Osborne and Stephen Jelley’s WSR BMW, but he was still leading the Independents class as the race went into its closing stages.
Catching Hamilton was Power Maxed Racing’s Mikey Doble, making his BTCC debut, and the Vauxhall Astra passed the Cupra into Redgate at the start of the penultimate lap, only for Hamilton to get back ahead at the top of the Craner Curves.
Hamilton’s bid for Independents victory became the focal point, but it was Doble who snatched it – and sixth overall – into the chicane on the final lap.
Doble and Hamilton were among those to be promoted one position when Pearson was excluded after his Hyundai failed the post-race ride-height check. That moved Osborne up to his maiden podium in third from Jelley, Doble and Hamilton.
Nick Halstead (Excelr8 Hyundai) was a lonely seventh, while Colin Turkington was the best-placed of those to pit for wets after the safety car, bringing his WSR BMW home in eighth.
Ninth was Ingram, who got ahead of Bobby Thompson (Team Hard Cupra) and Rowbottom in the final laps.
Rowbottom was classified 11th, the last driver on the lead lap, while late stoppers Cammish, Ash Sutton and Jake Hill were among those to be lapped during their pitstops.
But with the number 12 being pulled out in the reversed-grid draw, Pearson's exclusion handed a second pole of the day for the finale to Cammish, with Rowbottom alongside.
BTCC Donington Park - Race 2 results (21 laps)
| Cla | Driver | Car / Engine | Gap |
| 1 | Tom Chilton | Hyundai | |
| 2 | Adam Morgan | BMW | 7.394 |
| 3 | Ronan Pearson | Hyundai | 15.617* |
| 4 | Sam Osborne | Ford | 18.622 |
| 5 | Stephen Jelley | BMW | 22.322 |
| 6 | Mikey Doble | Vauxhall/TOCA | 35.360 |
| 7 | Nicolas Hamilton | Cupra/TOCA | 35.619 |
| 8 | Nick Halstead | Hyundai | 51.253 |
| 9 | Colin Turkington | BMW | 59.353 |
| 10 | Tom Ingram | Hyundai | 1'17.130 |
| 11 | Bobby Thompson | Cupra/TOCA | 1'18.439 |
| 12 | Dan Rowbottom | Ford | 1'18.641 |
| 13 | Dan Cammish | Ford | 1 lap /3.694 |
| 14 | Dan Lloyd | Cupra/TOCA | 1 lap /6.682 |
| 15 | Rory Butcher | Toyota | 1 lap /9.426 |
| 16 | Ash Sutton | Ford | 1 lap /15.817 |
| 17 | Jake Hill | BMW | 1 lap /18.765 |
| 18 | Aiden Moffat | Honda | 1 lap /24.000 |
| 19 | Dexter Patterson | Cupra/TOCA | 1 lap /37.612 |
| 20 | Josh Cook | Honda | 1 lap /48.686 |
| 21 | Árón T.-Smith | Vauxhall/TOCA | 1 lap /55.876 |
| 22 | Andrew Watson | Vauxhall/TOCA | 2 laps /2.000 |
| Will Powell | Honda | Retirement | |
| Jade Edwards | Cupra/TOCA | Retirement | |
| George Gamble | Toyota | Retirement | |
| Jack Butel | Cupra/TOCA | Retirement | |
| Ricky Collard | Toyota | Retirement | |
*Excluded for failing post-race ride-height check
