Hartnell's second man-advantage marker came on a blazing one-timer from the left circle off a feed from Claude Giroux. The tally gave Philadelphia a 3-1 lead 8 minutes into the third period.
Hartnell also scored in the middle frame, as did the Flyers' Matt Read, while Wayne Simmons added an empty-netter as Philadelphia rebounded from a Thursday loss to the last-place New York Islanders.
Ilya Bryzgalov earned the victory by stopping 30-of-31 shots, including 14-of-15 in a busy second period.
Alexei Ponikarovsky, acquired by the Devils from Carolina Friday, netted his first goal for New Jersey.
Martin Brodeur finished with 16 saves in the loss.
Swim Week Miami Beach 2014 [PHOTOS]