The discarded striker Danny Welbeck returned to haunt Manchester United by scoring the winning goal as Arsenal reached the FA Cup semi-finals with an enthralling 2-1 victory at Old Trafford.
England international Welbeck, who joined the Londoners last summer after his United career stalled, pounced on a poor back pass by Antonio Valencia in the 61st minute to send the holders through.
In an action-packed first half Nacho Monreal's cool finish put Arsenal ahead in the 25th minute but Wayne Rooney's diving header evened it up four minutes later.
United, who will now ponder a second consecutive season without silverware, ended the match with 10 men after Angel Di Maria was red-carded for grabbing the referee's shirt just seconds after being booked for diving.
Arsenal will play the winner of Bradford or Reading in the semi-finals, while Aston Villa will take on either Liverpool or Blackburn Rovers.