Philadelphia scored three times in the third period to record a 5-3 win over Wilkes-Barre/Scranton on Tuesday night.
The Phantoms have a 3-1 lead in the best-of-seven East Division final, and head back home on Friday with a chance to advance to the Eastern Conference championship series.
Joni Pitkanen, Patrick Sharp and Jon Sim scored in the third as Philadelphia held on after bringing a 2-1 lead into the final 20 minutes.
Mike Richards and R.J. Umberger had the other Phantoms goals.
The Penguins had allowed five goals in four previous home games during the postseason — all wins — but the Phantoms struck five times on 26 shots against Andy Chiodo.
Antero Niittymaki made 26 saves for the Phantoms.
Attendance was 7,227 at the Wachovia Arena.