Washington finished with 10 points and 10 rebounds, Jordan Downing added 15 points and both recorded six boards to help Presbyterian (5-16, 2-5) outrebound Longwood 33-26.
Down 61-51 at the 10:58 mark, Longwood went on a 9-0 run capped by two free throws from David Robinson to make it 61-60 with 7:05 remaining.
The Blue Hose answered with a 15-4 run, taking a commanding 76-65 lead on Mutakabbir's layup with just 1:32 left to play.
Presbyterian made four free throws and Longwood (3-18, 0-7) converted just one field goal in the final minute.
The Blue Hose completed all 16 of their free throws for the game.
Robinson and Michael Kessens scored 16 apiece to lead the Lancers, who have lost 11 straight games.
Who are the best NBA prospects in the 2017 draft class? Chad Ford gives his top five and previews the big storylines to watch for next year.
Cal shooting guard Jordan Mathews, who averaged 13.6 points as a sophomore, has decided to transfer to Gonzaga.
Maria Taylor and Peter Burns share the greatest moments of the year around the conference.