The Flyers, who led 2-0 after one period, saw their lead grow to 3-0 with another early goal when Erik Gustafsson ripped a shot past Marc-Andre Fleury at the 5:25 mark of the period.
The Penguins finally had an answer when Evgeni Malkin scored a crucial power play goal at the 8:34 mark.
But just as they have all series, the Flyers had a quick answer, as this Danny Briere goal just 1:26 later gave the Flyers the momentum back, and a 4-1 lead.
The Penguins, on the brink of elimination, have looked lost in the defensive end all afternoon. Although the Flyers have outshot the Penguins by only a slim margin of 20-19, the Penguins have never been able to get into a rhythm in the attacking zone.