Larsson and Clarkson scored consecutive goals in the third period to rally the Devils past the Flyers and make up for the absence of Ilya Kovalchuk. The Devils played without their regular-season leading scorer because of a lower body injury.
Travis Zajac added a late goal to make it 3-1, and Bryce Salvador scored a late empty-netter for the Devils.
Game 3 is Thursday in New Jersey.
Matt Read scored 2:53 into the game to give the Flyers hope they could jump to a commanding series lead. Instead, the offense went into a funk and goalie Ilya Bryzgalov couldn't protect the advantage.
Even without Kovalchuk, the Devils did what they wanted against Bryzgalov, taking close shots and dominating the play in the Flyers' zone.
They just couldn't score ... until the third.
Bryzgalov, who signed a $51 million, nine-year deal last summer, was especially stout in the second when he bailed out the Flyers offense with a 12-save period. The Flyers went more than 18 minutes in the period before taking a shot on Martin Brodeur.
"I didn't sense frustration. We were comfortable with how we played the first two periods," Devils coach Peter DeBoer said. "And it was just a matter of keeping it going in the third, and the goals came."
Bryzgalov had a brutal first five games of the postseason and allowed 20 goals against Pittsburgh. But he shut down the Penguins in the Game 6 clincher - a 5-1 win - and allowed three goals in the Game 1 victory against the Devils.
He appeared to have turned the corner.
Then came the final period.
Kovalchuk's injury opened a roster spot for Larsson, a rookie defenseman, to be activated. Larsson was a first-round pick last year, and is just 19 years old. He had two goals and 18 points in his first NHL season, but had not played a playoff game yet. Larsson's shot from the circle beat Bryzgalov on his glove side early in the third for the tying goal.
"Down a goal, third period, and it was huge," DeBoer said of the rookie's goal. "I feel great for Larsson. He's been out a few games, and he responded."
Clarkson made it 2-1 minutes later when he scored off a rebound. The Devils won the faceoff and Zach Parise was stuffed with a pad save. Clarkson then crashed the net to knock in the puck and fly gut-first into the crossbar. He lay on top of the net briefly as his teammates mobbed him.
Bryzgalov slammed his stick in frustration after the goal.
Zajac's fifth goal of the postseason on a backhander made it 3-1 and gave the Devils the insurance goal they needed.
"I really felt we'd respond like this," DeBoer said. "I knew we'd be better than Game 1. Knew we'd bounce back. We've dealt with adversity and injuries all year. It's nothing new."
Bryzgalov shook his head and remained motionless on his knees for at least a minute after Zajac's goal. He was still down on one knee for the faceoff before he finally stood up and got his head back into the game.
He clearly wasn't happy about the goals. And he was probably angry with Philadelphia's offensive ineptness, as well.
At the end of the game, Claude Giroux stopped Bryzgalov for a brief chat before he was greeted by the rest of the team. Giroux has emerged as the leader of the team and whatever he was telling the goalie, Bryzgalov seemed to agree with, mostly nodding his head.
The Flyers entered with an NHL postseason-high 34 goals but failed to generate much offense after a move-the-puck first 10 minutes.
Read scored from a tough angle outside the circle to beat Brodeur for the fast 1-0 lead. But it didn't hold up.
Not even Giroux and Danny Briere could spark the Flyers. Each tick of the clock in the second period was like watching a no-hitter to see if the Flyers would finally put the puck on Brodeur. With 1:27 left in the period, the Flyers broke through for a shot and they only took one more.
The Devils outshot them 12-2 in the second, in fact. And to make matters worse, the Flyers opened and closed the period on the power play.
The road win was New Jersey's third of the postseason.
"We knew, if we lost tonight, it wasn't going to look good for us," DeBoer said. "I'm not surprised to see us play the way we did."
Though clearly they missed Kovalchuk for long stretches. In his third season with the Devils, Kovalchuk has three goals in eight playoff games and remains day to day. He walked with a pad on his back after Sunday's 4-3 overtime, Game 1 loss, and walked around the locker room Monday at practice in Newark, N.J., quite gingerly.
Kovalchuk, a former Atlanta Thrasher who had 37 goals and 83 points this season, won his first playoff series ever in New Jersey's Round 1 triumph over Florida. The Devils say Kovalchuk was injured in that first-round series.
Defenseman Peter Harrold, who had three points and five shots on goal in the postseason prior to Game 2, was moved up to a forward position to replace Kovalchuk's spot in Game 2, allowing Larsson to play defense.
Notes: This was New Jersey's first regulation postseason victory since Game 4 against Florida, and just Philadelphia's second home loss of the playoffs. ... New Jersey has now won three of four games. ... Clarkson had 30 goals and 46 points in the regular season. ... Brayden Schenn had his fifth assist of the postseason on Read's goal.