With the victory, the Flyers slipped past the Penguins and into first place in the Atlantic Division and Eastern Conference.
Danny Briere, Wayne Simmonds, and Hartnell scored for the Flyers, who have four consecutive wins - all by Bryzgalov.
"We came out with the mind-set that we were playing for first," said Briere, who opened the scoring with a crazy first-period goal.
The Flyers were playing their second game in as many nights - Pittsburgh was rested - and they controlled the first two periods before running out of energy in the final 20 minutes.
But they survived.
"I liked our resiliency at the end," Laviolette said. "It wasn't our best last 10 to 12 minutes, but our guys really fought for it."
One night earlier, the Flyers scored a draining, 5-4 overtime win in Buffalo in which they overcame a 3-0 deficit.
Briere, who had played just 9 minutes, 22 seconds Wednesday because he was fighting the aftereffects of a virus, scored a gift goal Thursday - the ol' double-deflection shot - to give the Flyers a 1-0 lead after 6:38.
From a few feet above the left circle, Briere's blast hit off Penguins defensemen Robert Bortuzzo and Brooks Orpik - and went past stunned goalie Marc-Andre Fleury, who did the splits but couldn't reach the puck.
With 11:18 remaining in the second period, the Flyers made it 2-0 when Simmonds knocked in Jakub Voracek's goalmouth pass while on a power play.
"It's probably one of the easiest goals I've had in the NHL," Simmonds said.
Nearly five minutes later, defenseman Andrej Meszaros made a great move past Orpik in the Penguins' zone and crossed a pass to Hartnell, who, while falling down, tapped in his seventh goal in the last nine games. Hartnell has scored in four straight games.
Pittsburgh, playing without Sidney Crosby, got to within 3-1 on James Neal's power-play goal with 5:50 left in the second period.
Never mind that when he is healthy, Crosby is generally regarded as the best player in the NHL.
In his pregame news conference, Laviolette didn't want to talk about the Flyers' being fortunate to not face Crosby, who collided with teammate Chris Kunitz on Monday and was kept out of Thursday's game as a precaution.
Lavilolette wanted to talk about how lucky the Penguins were to oppose the Chris Pronger-less Flyers. Pronger is recovering from knee surgery.
Laviolette said he "found it odd that you didn't ask about Pronger not playing. Our captain is out of the lineup and we'll certainly miss him, and what a break for Pittsburgh."
As it turned out, the Penguins missed Crosby more than the Flyers missed Pronger.
The Penguins had little offense in the first two periods, and when they did have a cycle working, Bryzgalov stood tall.
Bryzgalov made his fourth straight start; he started both ends of two sets of back-to-back games in that stretch.
"If it had been a different opponent, maybe I would have considered something different," Laviolette said of his decision to start Bryzgalov. "But we want to get him going . . . and this was a big game. It was for first in the conference tonight."
Contact staff writer Sam Carchidi at firstname.lastname@example.org or @BroadStBull on Twitter.