Will Grigg scored twice for the home side as they capitalised on some poor errors from the visitors. To compound the humiliation, Arsenal loanee Benik Afobe came off the bench to score twice to overcome Louis van Gaal's side to dump them out of the competition, and give MK Dons their most high profile win in their 10-year history.
Though United boss Louis van Gaal made 10 changes to his side, there were still some household names on show.
Given that Afobe is on Arsenal's books having been sent on loan for a season, Gunners fans certainly seemed to enjoy what their young forward was doing to one of their Premier League rivals.
Here is a sample of what they had to say about their young forward's performance on twitter:
Benik Afobe goes on loan and still finds a way to destroy Man United's season. That's a true Arsenal boy right there!— Marshall Steele (@RealSteeleCity) August 26, 2014
we should bring back Benik Afobe imo. Need someone who can score against bottom half teams like Man United.— Aidán (@BeltransMole23) August 26, 2014
Arsenal loanee Benik Afobe grabbing a brace against Man United thrashing em 4-0. Nice. #Arsenal— Rohit Ramesh (@roh00) August 27, 2014
Joel Campbell and Benik Afobe, whatever may come of your Arsenal careers, I will always love you for the things you did to Man Utd.— Flánchez (@Flannyballs) August 26, 2014