Bamboo-engineering’s MacDowall was quickest with a time of 1:56.304 in a session that was interrupted by a red flag.
Cumbrian MacDowall said: “After the red flag we put a new set of tyres on and we made a few set up changes. It is a very difficult track to get used to. It has a low grip and when you put new tyres on you are quick for just one lap and then they go off dramatically. We have to work hard on the race set up.”
Rob Huff was second fastest, having completed a lap of 1:56.346, while Pepe Oriola and his SEAT were classified in third position with a time of 1:56.387 also posted in the final minutes.
WTCC returnee Colin Turkington climbed to fifth with a lap of 1:56.651, after the red flag had spoiled his previous attempt.
They were the only four drivers who were able to improve their times after the red flag that had been waved with eight minutes left on the clock to replace a pack of tyres hit by a car at Turn 11.
Tiago Monteiro’s Honda Civic was placed in a promising fourth position with a lap of 1:56.439 – only one tenth behind MacDowall’s time. The Portuguese driver had set the time shortly before the session was disrupted.
Yvan Muller (1:56.653) was sixth, followed by the fastest BMW of Tom Coronel (1:56.735), local hero Darryl O’Young (1:56.785), Tom Boardman (1:56.931) and Fernando Monje (1:57.184).
The third Chevrolet factory driver, Alain Menu (1:57.188), was 11th just ahead of James Nash’s Ford Focus (1:57.316).