Shorty after the start of overtime, Iginla broke into the Hurricanes zone, bursting through a pair of defenders before finding Krejci open in the slot.
Krejci steadied the pass, switched to his forehand and fired a shot past Cam Ward, lifting the Atlantic Division-leading Bruins to their third win in four games.
Zdano Chara and Reilly Smith also scored for Boston.
Chad Johnson earned the win with 22 saves.
The Hurricanes' Patrick Dwyer netted a shorthanded goal midway through the third period to forge a 2-2 tie.
Andrej Sekera scored and Ward finished with 35 saves for Carolina, which has dropped four straight games.