Tkachuk gave the Panthers a 1-0 lead at 1:15 of the first period when he redirected Carter Verhaeghe's centering pass.
Farabee tied it 1-1 at 4:43, tipping Noah Cates' shot past Lyon. It was Farabee's third straight game with a goal after he went 26 games without one.
Sanheim scored from the right side to put Philadelphia ahead 2-1 at 8:42 of the second period.
Montour tied it 2-2 at 14:17 after he pinched down from the right point and took a pass from Aleksander Barkov.
After the Flyers' late outburst in the second, Reinhart made it 5-3 on a power play at 13:49 of the third period with Lyon pulled for an extra attacker, but Frost scored an empty-net goal at 17:59 for the 6-3 final.
It was the Panthers' fourth game in six nights.
"I think [we were] just caught a little sleepy," Montour said. "I think at this point of the year, no matter how tired you are, you figure it out and you try to make the right plays. They bear down on some chances there and we couldn't get back."
NOTES: The Panthers were without forwards Anthony Duclair (illness) and Sam Bennett (undisclosed). Maurice said Bennett is day to day. ... Tkachuk has six goals during his five-game streak, and 15 points (six goals, nine assists) in a six-game point streak. ... Reinhart extended his point streak to six games (nine points; six goals, three assists). ... Barkov had two assists. ... Tortorella is one win from becoming the 12th NHL coach with 700 wins. He is 699-573-144 with 37 ties in 21 seasons with the Tampa Bay Lightning, New York Rangers, Vancouver Canucks, Columbus Blue Jackets and the Flyers. ... Philadelphia defenseman Egor Zamula, who was recalled from Lehigh Valley of the American Hockey League, had two assists in his first NHL game since Dec. 1.