Free of injury, Hewitt displayed his renewed court speed and trademark determination to upset Berdych 6-3 6-2 in just 88 minutes.
He will face the winner of the match between Argentine Juan Martin del Potro and Cypriot Marcos Baghdatis for the title.
Earlier, Canadian Milos Raonic defeated Croatian Ivan Dodig for his first win in the Classic.
The big-serving world No.15, who lost to Hewitt on the opening day, defeated Dodig 6-4 6-4.