Larsson, a rookie defenseman, notched his first career post-season goal 3 minutes into the final frame, pulling the Devils even at 1-1. David Clarkson scored with 9 minutes left, giving New Jersey its first lead, and Travis Zajac scored on a wraparound 3 minutes later for a 3-1 Devils advantage.
Bryce Salvador added an empty-netter and the Devils equalized their Eastern Conference semifinal series against the Flyers at one victory apiece.
Martin Brodeur earned the win, turning aside 19-of-20 shots.
Matt Read scored and Ilya Bryzgalov made 31 saves for Philadelphia, which couldn't keep up the momentum from its 4-3 overtime triumph in Sunday's Game 1.