Claude Giroux scored a power-play goal to extend his point streak to four games, and Brian Elliott allowed four goals on 15 shots for the Flyers (22-13-5), who went 2-5-0 on the road in December. It was Philadelphia's second loss in seven games.
"A staple of our team so far this year has been our penalty kill, and tonight it wasn't very good," Flyers coach Alain Vigneault said. "That combined with them scoring on our power play took us out of the game early. Tried to battle back, but we have a couple of guys right now who don't seem to have a lot of energy on the ice."
Kyle Clifford gave the Kings a 1-0 lead at 5:31 of the first period when he scored on a wrist shot from the left face-off circle.
Alex Iafallo made it 2-0 at 6:57 when he tipped Kopitar's pass on the power play.
"They were aggressive," Flyers defenseman Ivan Provorov said. "They were putting pucks at the net, and we just couldn't get to the loose pucks and couldn't get the rebounds. Their first goal on the power play was just a nice play, kind of nobody's fault. They skated right into an area and they hit him right away, so I don't think it was anybody's fault."
Tyler Toffoli put the Kings ahead 3-0 with a power-play goal at 8:45, following up his own rebound with a sharp-angled shot into an open net. Kopitar had the primary assist to pass Robitaille.
Adrian Kempe scored shorthanded at 17:52 for a 4-0 lead with a wrist shot from the right circle on a 2-on-1 rush.
Carter Hart replaced Elliott to start the second period and made 13 saves in relief.
Justin Braun cut the Kings lead to 4-1 at 14:59 when his centering pass deflected in off defenseman Matt Roy's skate.
Martin Frk scored on the power play to make it 5-1 on a slap shot from the left circle at 1:31 of the third.
Giroux made it 5-2 by chipping a one-timer over Quick at the far post at 7:16. He has four points (one goal, three assists) during his point streak.
Braun's shot from the point went in off Scott Laughton's skate at 17:08 for the 5-3 final.
"We did our best trying to climb out of it but just couldn't tie the game and force the OT," Provorov said. "For now, just learn from the mistakes and move on."