In arguably their worst 20 minutes of the young season, the Flyers watched the Penguins set up a shooting gallery for most of the second period. Pittsburgh outshot the Flyers in the period, 17-5, and got goals from Jussi Jokinen (after the Flyers had four chances to clear it) and Chris Kunitz (off a rebound).
But with two seconds left in the second, Wayne Simmonds tipped in Claude Giroux's floater - the Flyers captain looked up at the clock before shooting from the left circle - to cut the Penguins' lead to 2-1.
That snapped a funk in which they had failed on their last 18 power-play attempts.
At that point, Pittsburgh's 2-1 lead felt more like 7-1. The Penguins were that dominating, but only Mason's brilliance kept the Flyers close.
Before the game, Flyers coach Craig Berube stressed that his team needed to give a full 60-minute effort.
Afterward, he said that he got only 40 minutes and that it was "very surprising and disappointing" that his team couldn't play three solid periods against its bitter archrival.
"We were standing around," he said of the middle period.
"The second period was awful and we never really recovered from it," said Simmonds, who was minus-4 in the game. "We were brutal. We weren't executing, we weren't getting pucks deep, we were turning pucks over in the neutral zone. They're a good transition team, and we couldn't get pucks out of our own zone - and they took advantage of it."
Simmonds' goal, his first of the year, jump-started the Flyers and they dominated the third period but couldn't score the equalizer. Sidney Crosby locked it up by tipping in a shot with 2:32 left, giving him points in all seven games.
Evgeni Malkin added an empty-net goal.
Mason made 31 saves, some of which were acrobatic.
"He's standing on his head every single game," Simmonds said. "It [stinks] for him because we're not supporting him down the other end."
For all their shortcomings, it's remarkable that the Flyers could have a winning record if they had played better in the third period of their games. They have been outscored, 12-2, in the third period.
In each of their first eight games, they have either been tied, had a lead, or trailed by one goal entering the third period.
The Flyers entered the third period facing a 2-1 deficit Thursday and failed on two power plays early in the period. In one of them, Marc-Andre Fleury made a sensational glove save to rob Simmonds from point-blank range. Simmonds rolled his eyes and looked up at the rafters in disbelief.
About 31/2 minutes later, with the Flyers on another power play and 15:13 remaining, Brayden Schenn pounced on a rebound but fired wide with an empty net in front of him.
Flyers defenseman Kimmo Timonen (minus-2) left the game with an undisclosed lower-body injury late in the second period and did not return.
Earlier in the day, Giroux said the game was critical for the home team.
"Tonight's going to be a game to bring the fans back on our side and show them that we're a good team and can win games," Giroux said in the morning, calling the contest a "turning point."
Instead, it turned into another hard-fought loss.