The double champion held the lead at the start, and then led home Sutton after an untroubled run. In fact, the only mistake made by either driver was a bungled attempt to give Sutton a bonus point by letting him lead a lap: they made the switch just after the official timing line, so it didn't count.
Plato reckoned his improvement in form was down to discovering a problem with the car’s differential, which he believes was the cause of his season-long struggles, after qualifying. “It was like a different car in this race,” he said.
Turkington claimed the final spot on the podium – and with it the points lead - ahead of his WSR BMW team-mate Rob Collard.
The undulating Knockhill circuit clearly suited rear-wheel-drive cars, with James Cole battling up to fifth in his Subaru. Ingram finished sixth – and top front-wheel-drive runners – in his Toyota Avensis.
Matt Neal put in a storming drive in his works Honda Civic Type-R, charging from 21st on the grid to ninth place. His title-chasing team-mate Gordon Shedden finished 11th in his ballast-laden car.
Driven: Honda's 2017 BTCC racer - includes video
Plato and Sutton dominated again in the second race, although this time the positions were reversed.
While Plato, carrying the maximum 75kg of ballast on his Levorg, got away well from pole, Sutton bided his time before dragging past him on the main straight midway through the race. Plato kept the pressure on his young team-mate but couldn’t find a way back past. Sutton's fifth victory of 2017 moved him to within two points of Turkington in the title battle.