After spotting Ottawa an early 2-0 lead, Marcel Goc began a Florida comeback 33 seconds into the middle frame with a tip-in of a Mike Weaver shot.
Krys Barch scored the equalizer 2 1/2 minutes later, and with Chris Neil off on a high-sticking penalty midway through the period, Samuelsson converted a feed from Stephen Weiss for the eventual game-winner.
Jack Skille added a goal and an assist.
Jose Theodore stopped 23-of-25 shots for the Panthers, who padded their division lead over idle Winnipeg to four points with the win.
Neil and Jared Cowen scored for the Senators, whose nine-game unbeaten streak against Florida was snapped.
Robin Lehner made 24 saves for Ottawa, which holds the seventh seed in the Eastern Conference.