Jay Bouwmeester, Montador, Rostislav Olesz and Kamil Kreps scored for the Panthers, who have lost three in a row and five of six. The Panthers gave up goals in the final minute of their previous two losses, at Carolina and Pittsburgh.
The Panthers led 4-2 after two periods despite being outshot 30-12. Boston finished with a 48-27 advantage in shots on goal.
Boston tied it midway through the third period with two goals in a span of 1:38.
Chara scored on a power play at 13:10 when he one-timed a cross-net pass from Sturm. Kessel then beat Tomas Vokoun, who made 44 saves, with a wrist shot from the top of the faceoff circle at 14:48.
Florida scored three times on seven shots in the second period to extend their 1-0 lead. Kreps scored the final goal with 0.8 seconds left when he beat Thomas on a 2-on-1 with a wrist shot to the short side.
Thomas, who came in second in the NHL with a .926 save percentage, was pulled after giving up four goals on 12 shots.
The Panthers broke a 1-all tie with two goals in 2:39 midway through the second period.
Montador scored at 9:32 when he took a centering pass from Olesz in the slot and beat Thomas low to the glove side.
Then after Boston’s Marc Savard hit the post with a shot from a sharp angle, Olesz increased Florida’s lead at 12:11, beating Thomas with a wraparound goal after holding on to the puck on a 3-on-2 rush.
Wideman made it 3-2 at 16:13 when Wideman beat Vokoun with a slap shot from the point on a power play.
Boston C Savard had two assists. He came in with a league-leading 52 assists. … Boston LW P.J. Axelsson played his 700th NHL game. … Boston is now 3-0-1 on a five-game road trip that ends Saturday at Tampa Bay. … The loss kept Jacques Martin from reaching his 100th victory as Panthers coach. His record with Florida is 99-94-34.