Four power-play goals sparked Pittsburgh to an 9-3 lead over the Flyers Wednesday after the first two periods.
Jordan Staal had a hat trick heading into the final period.
Barring a total collapse, Pittsburgh will cut the Flyers' lead to three games to one. Game 5 would be in Pittsburgh on Friday.
The Pens got second-period PP goals from Kris Letang, Jordan Staal and Steve Sullivan, quieting the sellout crowd at the Wells Fargo Center.
Letang's goal with 16:53 left in the second period chased Ilya Bryzgalov (five goals on 18 shots). Sergei Bobrovsky replaced Bryzgalov, who has not looked the same since suffering a chip fracture in his right foot late in the season.
Pascal Dupuis increased the lead to 8-3 with 5:01 left in the second, and Staal completed his hat trick a little over a minute later.
Defenseman Matt Niskanen scored a power-play goal _ a one-timer from the left circle _ to give Pittsburgh a 2-1 lead with 11:55 left in the first period Wednesday night at the Wells Fargo Center.
Claude Giroux (1:16) and the Penguins' Evgeni Malkin had traded goals in the first 3:27 as the teams were in an early 1-1 tie.
It was Giroux's fifth goal of the series, and Malkin's first. Malkin charged out of the penalty box and scored on a juicy rebound allowed by Bryzgalov.
Giroux, Kimmo Timonen and Jake Voracek each had first-period power-play goals for the Flyers. ASfter the opening period, the Flyers were a ridiculous 9 for 15 on the PP in this series.
With a loss, the Penguins would have become the second team in the NHL's 94-year history to be swept in the first round after collecting 50-plus wins in the regular season.
The Flyers' lineup:
Coburn-Grossmann; Carle-Timonen; Kubina-Lilja.
The Pens' lines:
Kunitz-Malkin-Kennedy; Sullivan-Crosby-Dupuis; Tangradi-Staal-Cooke; Jeffrey-Vitale-Park.