PITTSBURGH — The Philadelphia Flyers fell behind. Again. And it didn’t matter. Again.

Who needs the first period anyway? Not the Flyers, who keep finding increasingly inventive ways to stun the Pittsburgh Penguins.

Claude Giroux had three goals and three assists to set a franchise record for points in a playoff game, rookie Sean Couturier had a hat trick of his own and Philadelphia rallied for a wild 8-5 victory last night in Game 2 of the Eastern Conference quarterfinal series.

Two nights after turning an early three-goal deficit into a 4-3 overtime win, the Flyers were even more impressive while taking a 2-0 lead in the best-of-seven series.

The Penguins had leads of 2-0, 3-1, 4-3 and 5-4 at home and still couldn’t fend off Philadelphia, which did a little bit of everything.

The Flyers scored a pair of short-handed goals, added one on the power play and threw in an empty-netter to push a Pittsburgh team considered a Stanley Cup favorite to the brink.

“I don’t know how many times we’ll be able to do comebacks like that,” Giroux said. “We’ve got to have a better start.”

At this point, why bother?

Philadelphia scored seven goals in the game’s final 35 minutes, responding every time it appeared the Penguins were finally ready to take control. Jaromir Jagr and Max Talbot — both Cup winners in Pittsburgh — also scored for the Flyers, who host Game 3 tomorrow.

“This team can always score goals,” said Jagr, who gave Philadelphia its first lead in regulation in the series midway through the third period. “We’ve got a lot of guys who can score goals.”

Including the 19-year-old Couturier. Assigned to slow down Pittsburgh’s Evgeni Malkin, Couturier outscored the Russian instead for the first hat trick by a Philadelphia rookie since Andy Delmore in 2000.

Couturier admitted to feeling some jitters before the series opener. Funny, he hardly looked nervous when his third goal of the night sewed it up with 1:49 remaining before Giroux’s empty- netter completed the scoring.

“He’s 19, but he plays like he’s 28,” Giroux said.

Ilya Bryzgalov overcame another shaky start to stop 23 shots for the Flyers, who never blinked after getting down by multiple goals for the ninth time in their last 14 games.

“You have a choice to win the game or give up,” Bryzgalov said.

Chris Kunitz had two goals for Pittsburgh, and Sidney Crosby and Tyler Kennedy scored for the second straight game, but the Penguins again failed to close out the Flyers.

The Penguins tried to downplay their collapse in the opener, insisting there was plenty of hockey to play.

Perhaps, but there might not be much left after another stirring comeback by the Flyers. Philadelphia is 17-0 when it wins the first two games of a series.

“We’ve got to find a way to be better with the lead,” Crosby said. “We know they’re going to keep coming.”

The Flyers proved it in the third period after Kennedy’s goal put the Penguins up 5-4.

It took Philadelphia just 17 seconds to respond, as Couturier created a turnover and broke in alone on Marc-Andre Fleury. The score seemed to suck all the energy out of the Consol Energy Center and what little remained disappeared when Jagr put the Flyers in front for the first time with less than 11 minutes to go.

“We need to limit our mistakes, that’s really what it comes down to,” Crosby said. “The mistakes we’ve made have ended up in our net.”

The ending was in stark contrast to another electric start by the Penguins.

Crosby needed all of 15 seconds to give Pittsburgh the lead, working a give-and-go off the opening faceoff with Steve Sullivan and ripping a one-timer by Bryzgalov. The goal tied Pittsburgh’s franchise mark for fastest goal to start a playoff game, set by Greg Malone against St. Louis in 1981. It also was the quickest allowed by Philadelphia opponent in playoff history, breaking the mark of 21 seconds set by Chicago’s Jim Pappin in 1971.

The lead grew to 3-1 by the end of the first period.

Yet just like Wednesday — when the Penguins led 3-0 after the first 20 minutes — it wasn’t nearly enough.

The Flyers rallied to tie it at 3 behind Giroux, who scored on the power play then beat Fleury with a wrist shot for Philadelphia’s second short-handed goal of the night.

The tie lasted all of 6 seconds, or as long as it took Kunitz to pounce on a rebound and slide the puck into the open net.

Still, the Flyers wouldn’t back down. Couturier tied it at 4 just before the second intermission horn, erasing all of Pittsburgh’s momentum and setting the stage for another victory by the NHL’s most resilient team.

“When you’re able to come back in a game like that again it speaks volumes about character in the room,” Philadelphia coach Peter Laviolette said. “Fighting back like that is not easy.”