Rask improved to 9-1 against Florida in helping Boston win for the third time in its last seven home games. The Bruins have won five straight and seven of their last eight against the Panthers.
Florida has lost 10 of its past 11 games and is on its longest skid (0-3-4) since a 10-game slide in April 2011.
''It's embarrassing,'' Panthers forward Shawn Matthias said. ''I can't remember the last time we won. There are no positives right now.''
Thomas is out with a lower body injury, but received a rousing ovation when he was shown on the Jumbotron midway through the third period. He played for the Bruins from 2002-12, leading Boston to the Stanley Cup title in 2011 and winning the Conn Smythe Trophy as the postseason's most valuable player.
Thomas lost to Boston 3-2 in Florida last month, but has yet to oppose the Bruins at the TD Garden at any point in his career.
Brad Marchand had the winner on a wrist shot 4:09 into the third period, snapping a 12-game drought without a goal for Boston.
''Nice to finally get one,'' Marchand said. ''I forgot what it felt like, but nice to get the monkey off my back. It's frustrating because you want to contribute.''
Torey Krug gave Boston a 3-0 lead when he wristed home Chris Kelly's pass at 8:57 of the third for his sixth goal of the season.
''We seemed to get better as the game wore on,'' Bruins coach Claude Julien said. ''The third was definitely our best period. Sometimes when your team is struggling it is better to not say anything and just let the players work their way out of it.''
Boston was 1-3-1 in its last five and hosts division rival Toronto on Saturday in a rematch of the Eastern Conference Quarterfinals.
''We have spells we drop off during the game,'' Panthers defenseman Brian Campbell said. ''It's not fun. I'm not going to say we are having a good time. It's unacceptable.''
Reilly Smith capped the scoring for the Bruins at 18:13 of the third with an unassisted goal.
Clemmensen made 26 saves for Florida in his second start this season.
Florida's only road victory this season came against Dallas on opening night. ... Boston has outscored Florida 19-2 over the last four home games and Marchand has notched nine points. ... Florida began the night tied with Buffalo for allowing most goals in the Eastern Conference with 53. ... Winchester flattened Kelly with an elbow to the face five minutes into the game causing him to briefly leave the game.