Stephen Weiss had given the Panthers the lead with a tally in the top of the third round, but Patrice Bergeron -- who notched both of Boston's regulation goals -- forced a fourth frame when he got one past Scott Clemmensen.
Florida's Mikael Samuelsson then missed the net and Krejci iced the victory with a shot between Clemmensen's pads, handing the Northeast Division-leading Bruins their fifth win in eight games.
Tuukka Rask turned aside 38-of-40 shots for Boston.
Jason Garrison and Shawn Matthias scored for the Panthers, who lost for the fourth time in five games but pulled into a tie with Washington atop the Southeast Division with the single point.
Clemmensen finished with 33 saves.