The Bruins have paid the price for their turnovers and their undisciplined play.
Not only are the Bolts 2/2 on the power play through 40 minutes, but they also found the back of the net on a penalty shot.
Steven Stamkos was hauled down by Bruins forward Brad Marchand in the second period.
The Lightning sniper was unable to get a shot off on the play, and the referee awarded a penalty shot.
The 26-year-old made no mistake as he froze Tuukka Rask before burying the puck.
Stamkos has scored a goal in six straight games.
The Bolts lead 4-1 after two periods.