Giroux redirected a backhand shot from Nicolas Aube-Kubel to give Philadelphia its first lead of the game after falling behind 3-0 early in the first period when Pittsburgh scored three times in 1:11.
"Shortened season like this, obviously you look at the standings and a lot of teams are pretty tight," Giroux said. "For us to make the [Stanley Cup] Playoffs, we need to win games like tonight. I think the way we answered tonight, we're down 3-0, I think it's our first comeback win this year. So it's good to know we can do it, and that's how we need to respond in the future."
Giroux had two goals and an assist, and Brian Elliott made 26 saves for the Flyers (12-5-3), who have won four of five games. They lost 5-2 to the Penguins on Tuesday in the first of a three-game set.
Sidney Crosby had an assist after missing one game while in the NHL COVID-19 protocol, and Tristan Jarry made 31 saves for the Penguins (12-9-1), who have lost three of five games.
"I think when you have a great start like that, it's something that has to fuel you to keep bringing the same game that you're playing," Crosby said. "Unfortunately, they pushed back. We didn't."
The teams are scheduled to play again here Saturday.
Scott Laughton had a shot from Giroux go in off his leg to tie the game 3-3 at 13:37 of the third period.
"[Giroux is] our captain. He's our leader," Laughton said. "He brings us into the fight. ... He gets a goal late for us there. He takes big face-offs. He kills penalties. He's on the power play. He does a lot for our group. So I'm happy to see him get rewarded with two tonight."
Elliott made a glove save on Evgeni Malkin from in close with 9:46 remaining to keep the Flyers within one.