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.
Source: Autosport