Krejci picked up a loose puck after teammate Zdeno Chara had let it get away in front of the net and rifled a shot past Martin Brodeur. The defending Stanley Cup champions have a three-point lead over Ottawa atop the Northeast Division.
Krejci opened the scoring 1:13 into the contest and tied the score 3-3 early in the third period. He has 16 goals for the season.
Tim Thomas made 28 saves in Boston's third win in seven games.
Brodeur allowed all four goals on 25 shots in New Jersey's third loss in four outings. The Devils currently hold down the next-to-last playoff spot in the Eastern Conference.