Giroux, Sean Couturier and Dale Weise also scored for the Flyers, who closed within five points of the idle New York Islanders for the final playoff spot in the Eastern Conference. Making the postseason remains a long shot for Philadelphia with just 13 games remaining and four teams to pass.
The Flyers snapped a three-game losing streak while handing the defending Stanley Cup champions their fourth shutout of the season.
''For us, it's frustrating coming to the rink every day knowing we're a better team than what we are in the standings,'' Giroux said. ''We have some games left here and we're not going to stop.''
The road-weary Penguins completed an eight-day, five-game road trip that took them through four time zones as they traveled 4,763 miles. The journey got longer due to Tuesday's snowstorm in the Northeast, which caused the Penguins to fly home from Calgary on Tuesday rather than directly to Philadelphia. Pittsburgh arrived in Philadelphia late Wednesday morning.
But the Penguins didn't use the travel as an excuse.
''I think everyone's been in different situations over the course of their career,'' Sidney Crosby said. ''Sometimes it's not perfect, but you've still got to go out there and perform, so I don't think we're going to use that as an excuse.''
With 95 points, Pittsburgh remained two behind idle Washington for first place in the Metropolitan Division and the best record in the NHL.
''We knew this was going to be a tough one coming into it,'' Penguins coach Mike Sullivan said. ''We obviously didn't have the juice we normally have, but give the Flyers credit. They played extremely hard.''
Mason posted his third shutout of the season and the 33rd of his career. He saved some of his best work for late in the game, making three strong stops within four minutes of each other with under 10 minutes remaining.
First, he denied Oskar Sundqvist's short-handed chance from right in front with 9:55 remaining. Then, Mason made a good pad save on Nick Bonino with 6:48 left before fully extending his left pad to deny Ian Cole's slap shot.
''It's the type of effort we needed every game, really,'' Mason said. ''That's the type of hockey that dictates how you win hockey games.''
Simmonds scored his 29th of the season and 200th of his career while tying teammate Brayden Schenn for the NHL lead with his 15th on the power play with 13:40 left in the second period to put Philadelphia up 2-0. Shayne Gostisbehere took the initial shot and Simmonds put the rebound over a sprawling Matt Murray.
''It's pretty cool,'' Simmonds said about getting his 200th goal. ''I never would have thought I'd play in the NHL, never mind 200 goals. It's even better we got the two points.''
Couturier put Philadelphia on the board a minute into the second when he also went high over Murray from close range after the puck deflected to him right in front of the net.
Murray had to go to the bench with 11:34 left in the period when he was inadvertently hit in the head by Philadelphia's Travis Konecny, but was able to stay in the game.
Murray finished with 24 saves.
Giroux scored on a wrist shot from the slot that beat Murray with 4:16 left, and Weise finished the scoring with 47.3 seconds remaining.
The game featured the return of defenseman Mark Streit, the former Flyers assistant captain who was traded by Philadelphia on March 1.
NOTES: Flyers D Brandon Manning (upper body) missed his second straight game and forward Jordan Weal (lower body) also was out of the lineup. ... Penguins forward Matt Cullen returned to the lineup after missing three straight games due to a lower-body injury. D Ron Hainsey (lower body) was injured and didn't play in the third period. ... Philadelphia Eagles quarterback Carson Wentz received a loud ovation when he was introduced while attending his first Flyers game. ... The Penguins lead 2-1 in a season series that wraps up March 26 in Pittsburgh. ... Crosby remained one assist shy of tying Jaromir Jagr for second place on the Penguins' all-time list. Crosby has 639 assists. Mario Lemieux owns the club record with 1,033.
Penguins: Return home to host the New Jersey Devils on Friday night.
Flyers: Play the second game of a back-to-back at New Jersey on Thursday night.
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