All four defeats have come against opponents in the Northeast Division, where the Bruins' lead has been sliced to two points.
Gratton started the scoring 4:50 into the opening period, then set up goals by Taylor Pyatt, Dumont and Stu Barnes as the Sabres ended a three-game winless streak. His other four-point night came in Buffalo while with Tampa Bay on March 19, 1995
Martin Biron made 27 saves to help Buffalo defeat Boston for just the second time in the last nine meetings (2-6-1).
Joe Thornton set up both goals for the Bruins, who had not dropped four in a row since last Feb. 28-March 6.