Turkington was drawn on pole position for the reversed grid, got the jump at the start, survived a restart following an early safety car and was never threatened en route to his milestone BTCC race win.
The West Surrey Racing-run BMW 330i M Sport crossed the line 4.096 seconds clear, although the gap was up to 4.8s with two laps remaining.
Dan Rowbottom, who earlier in the day clinched the Jack Sears Trophy title for drivers who had never scored a BTCC podium before 2021, held an early second place from the front row in his Team Dynamics Honda Civic Type R.
But Rowbottom was one of three drivers given a five-second penalty for being out of position at the start, and had a queue of cars behind him following the restart.
Jake Hill, who recovered superbly across the day from his clash with Adam Morgan in the opening race, eventually prised an opening on the 11th lap of 18.
Rowbottom had got into a squirm on the Craner Curves, and Hill used his momentum through the Old Hairpin to slide his Motorbase-run MB Motorsport Ford Focus up the inside into McLeans.
Josh Cook tried to take advantage to slip past Rowbottom in his BTC Racing Honda, but a clash between the two Civics on the run to Coppice allowed Aiden Moffat to take advantage and pass both in his Laser Tools Racing Infiniti Q50.
Moffat then applied pressure to Hill, who eventually claimed second, but had no answer to Turkington, whose 60th BTCC win equals the tally of fellow four-time champion Andy Rouse.
“Even starting on pole, there’s no guarantee what’s going to happen,” said Turkington.
“But as you see so often, when you get out front the car handles better and it’s so much easier.
“I just got a great start and a great restart, and I could pump the laps in.”
Rowbottom held onto fourth on the road ahead of Rory Butcher’s Speedworks Motorsport Toyota Corolla and Cook. But Rowbottom’s penalty slipped him to sixth, while Butcher claimed fourth despite carrying 57kg of success ballast with Cook promoted to fifth.
Jake Hill, MB Motorsport Ford Focus ST
Photo by: JEP / Motorsport Images
Dan Lloyd ran on the back of this group in his Power Maxed Racing Vauxhall Astra – he was one of those penalised for a start infringement, but the 5s addition had no effect on his seventh place.
It was close though, because championship leader Ash Sutton fell just 0.3s short of overhauling Lloyd on corrected times.
Sutton confessed to an error that ran him wide at Redgate on the opening lap, and caused double Donington winner Gordon Shedden to brake in avoidance.
Sutton then spent much of the race with his LTR Infiniti bottled up behind the Excelr8 Motorsport Hyundai i30 N of Tom Ingram, who was carrying the maximum 75kg of ballast.
The Infiniti finally got past the Hyundai with six and a half laps to go, by which point Sutton was 8.4s adrift of Lloyd, and he ran out of time to erase the gap further.
Stephen Jelley (WSR BMW) was another to pass Ingram, and he took ninth, while Shedden was consigned to 13th.
The safety car was caused when Sam Smelt speared across the road in the first-corner battling at Redgate and collected the unfortunate Jack Butel.
The result means that Sutton goes to the final round at Brands Hatch in a good position to claim his third BTCC title, although three other drivers are still in contention.
Sutton leads the way from Turkington by 32 points, with Ingram 38 adrift and Hill 45 behind, with a maximum of 65 points available across the weekend.
BTCC Donington Park – Race 3 results – 18 laps