"I missed one earlier when I kind of had an empty net on a rebound," Hartnell said of a second-period opportunity, "and I was lucky enough to get one back."
For Hartnell, it was his eighth goal and second game-winner of the season.
"It was a playoff atmosphere in here tonight," he said after the Flyers reached the 20-win mark on their earliest date since 1986. "You could just feel the intensity out there, and we played a solid game. . . . I think we controlled the game five-on-five."
The Flyers outshot the Penguins, 37-23. Pittsburgh managed just 14 shots in even-strength situations.
"The only chances they really had were on the power play," goalie Brian Boucher said. "And we had a huge [penalty] kill at the end. The guys had a couple of big blocks and forced shots wide."
It was Pittsburgh's first regulation loss since a 7-4 defeat by Boston on Nov. 10. The Pens had been on a 14-0-1 run and were trying to set a franchise record with an eighth straight road win.
Instead, the Flyers, who are one point ahead of the Penguins, extended their run to 8-1-3 and their points streak to six games.
The Flyers dictated the pace early and improved to 20-7-5. They were 15-16-1 at the same point last season.
"With the playoff run and all the rest of that, it was a great learning experience for a lot of our guys in here - and we've been able to carry it over into the season," Pronger said. "We got off to a lot better start, and we continue to push ourselves to get better. That's what it's going to take for us to go all the way."
Evgeni Malkin, who had missed the previous four games with a knee injury, scored a pair of power-play goals for Pittsburgh, which had a six-on-four late in the game but was stymied by the Flyers' penalty killers.
A sensational goal by the much-maligned Nik Zherdev gave the Flyers a 2-1 lead with 7:32 left in the second period.
James van Riemsdyk hit Zherdev with a pass in the neutral zone, and the speedy winger raced into the Penguins' end and undressed defenseman Brooks Orpik with a gorgeous move in the left circle. Zherdev circled to his right and fired a shot from the low slot over the right shoulder of Fleury for his 10th goal.
Zherdev, who spent most of the night on a line with Jeff Carter and van Riemsdyk, had been a healthy scratch in the Flyers' previous game, a 2-1 overtime win in Boston on Saturday. He played Tuesday instead of Jody Shelley, who began a two-game suspension.
During their previous 12 games - all wins - the Penguins had never trailed heading into the third period. Malkin tied it 3:18 into the final period.
Just because they took a long winning streak into the game, the Penguins weren't an overconfident team.
"Every game against Philadelphia is always intense, and there's always a little bit of something extra, especially with the way the two teams are now," Penguins superstar Sidney Crosby said before the game. Crosby extended his points streak to 19 games with a pair of assists. "Both teams bring out the best in each other."
The Flyers are 3-1 against the Penguins - with all three wins by 3-2 scores.
"We get to enjoy it for about three minutes and then move on and start thinking about Montreal," said coach Peter Laviolette, referring to the Flyers' rested opponent on Wednesday at the Bell Centre.
Contact staff writer Sam Carchidi at 215-854-5181 or firstname.lastname@example.org. Follow him on Twitter at www.twitter.com/BroadStBull.