Arsene Wenger's final match at Old Trafford as Arsenal manager ended in a 2-1 defeat with a stoppage-time header from substitute Marouane Fellaini earning the points for second-placed Manchester United.
Paul Pogba drove United into the lead in the 16th minute, pouncing after Alexis Sanchez had headed a Romelu Lukaku cross against the post.
Arsenal, fielding a largely second-string side, drew level in the 51st minute when Henrikh Mkhitaryan, signed from United in January, beat David de Gea with a well-placed effort.
United's Marcus Rashford had the ball in the net in the final minute but the effort was ruled out for offside before Fellaini headed in the stoppage-time winner from an Ashley Young cross.
Watch the highlights in the video above