After suffering a delaminated tyre in race one, Rowbottom had battled his Motorbase Performance-run Ford Focus ST from the back of the grid to 11th on the road in the sequel.
That should have given him second on the grid for the finale, but a three-place grid penalty forced him to start from fifth.
Rowbottom got up to fourth at the start, then speared inside the Speedworks Motorsport Toyota Corolla of Ricky Collard at Segrave on lap two to claim third.
The following tour, he tried a move on Aiden Moffat’s second-placed One Motorsport Honda Civic Type R at Segrave, but it failed to come off and the lack of momentum allowed Collard back ahead around the outside of Noble, only for Rowbottom to repass the Toyota at Church Corner.
Rowbottom soon hunted down Moffat again and, on the fifth lap, went around the outside of the Scot into the Complex to claim the inside line for Cobb and second place.
At this point Adam Morgan was over two seconds to the good in the West Surrey Racing BMW 330e M Sport he had started from pole position, but there were still 11 laps remaining.
By the end of the ninth of 16 laps, Rowbottom was with the Lancastrian red-head, and drew alongside the BMW at the fast Village right-hander before claiming the inside line for Church.
Rowbottom drew away to victory, while Morgan wasn’t too far ahead of third-placed Moffat by the finish.
Moffat faced immense pressure for most of the race from the WSR BMW of Colin Turkington, who twice tried a move around the outside of Noble, but in turn had to keep a careful eye on the mirrors for Collard.
Behind the leading quintet, Aron Taylor-Smith claimed a strong sixth in his Power Maxed Racing Vauxhall Astra.
A huge pack behind was headed by Rory Butcher’s Speedworks Toyota from Dan Cammish (Motorbase Ford), Tom Ingram (Excelr8 Motorsport Hyundai i30 N), Jake Hill (WSR BMW), Josh Cook (One Honda) and Ash Sutton (Motorbase Ford).
