Capt. Gabe Roder says a garbage can was set ablaze in the Malkin Bowl Road area at around midnight, but the more devastating blaze broke out 20 minutes later in Brockton Oval.
He says the 85-year-old Brockton Oval pavilion has been hit and damage is estimated at $200,000.
Crews had trouble fighting the fire in the old building, which was restored in 1987, because flames had worked their way into the roof.
Police have been searching for a firebug since two blazes in the park earlier this year, including a deliberately set fire on June 22 that destroyed the replica station of the popular miniature train exhibit.
No arrests have been made in connection with any of the fires. (The Canadian Press)