Andy Hilbert scored for the Islanders, who dropped their fifth straight game.
Biron made 38 saves and has beaten the Islanders 10 straight times. He made a brilliant glove save on Jack Hillen late in the first period. He also thwarted a breakaway attempt by Sean Bergenheim late in the second period.
It was Biron's first win since he beat Toronto 4-1 on Jan. 10. Since then he was 0-4, allowing 17 goals in 13 periods before Saturday.
Biron was lifted in his last start after allowing three goals in the first period at Boston on Feb. 7 in a game won by the Flyers 4-3.
Yann Danis had 29 saves for the Islanders.
The Flyers scored twice within 44 seconds early in the first period and added two other goals within 13 seconds midway through the third.
Giroux put the Flyers ahead with a one-timer at 5:00 of the first period after taking a pass from Upshall.
Hartnell made it 2-0 when he deflected Jeff Carter's wrist shot from the right circle at 5:44.
Hilbert got the Islanders within 2-1 with a wrist shot from the top of the left circle at 6:15 of the third period.
Carle scored unassisted at 9:10, Asham was credited with a goal when the puck nicked off his skate at 9:23, and Gagne scored on a penalty shot at 10:17.
The Flyers recalled Scott Munroe from the Philadelphia Phantoms, their American Hockey League affiliate, to serve as Biron's backup in place of Antero Niittymaki who is out with the flu.
Notes: New York was without C Doug Weight (MCL sprain), D Mark Streit (upper-body sprain), and RW Trent Hunter (hip flexor), among others. ... Islanders C Mike Comrie played in his 500th NHL game. ... Philadelphia C Carter has six points (two goals, four assists) in his past four games. ... The Flyers have beaten the Islanders seven straight times at home. New York has not won in Philadelphia since April 7, 2007.
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