During the 1989–90 season Harris was involved in the match looked upon as saving Alex Ferguson's Old Trafford career, the FA cup third round tie between Nottingham Forest and Manchester United in which Harris acted as a linesman. The match was believed to be important as after some seven games without a win, should Manchester United lose this game Ferguson would be sacked soon after, this being his last chance to get a win. During the second half of the match Mark Robins scored for Manchester United, but with only three minutes of the match remaining Nottingham Forest felt they had equalized when following a goalmouth scramble the ball found its way into the Manchester United goal. The referee immediately gave the goal until Harris flagged for an infringement against Nottingham Forest and the goal was disallowed, Television replays after the match were unable to discover the reason for his decision and what he could have seen from his position on the line. With Manchester United winning the match 1-0 they went on to win the FA cup that season, giving Ferguson his first major trophy as their manager.