The game lacked quality for large periods but two second half goals, a fantastic Craig Gardner free-kick and a well-taken solo effort from James McClean, secured a safe passage into round four for Sunderland.
Martin O'Neill saw his captain Lee Cattermole sent off for the fifth time in his Sunderland career for a nasty first-half challenge on MK Dons defender Adam Chicksen but the Barclays Premier League outfit still had just enough in reserve to see off their npower League One hosts.
Neither side could keep hold of the ball for a prolonged period of time and no-one could produce a clear-cut chance in the search for an early breakthrough.
A touch of class was injected into proceedings in the 18th minute when Sunderland winger McClean's piece of skill on the touchline beat three Dons defenders.
The Republic of Ireland international continued his run into the penalty area and his effort was deflected into the path of Louis Saha, whose firm shot was well saved by goalkeeper Ian McLoughlin.
Moments later the former Tottenham striker, making his first start for Sunderland, had another chance to open his account for the club but bent a curling effort past McLoughlin's far post.
It was the home side who came close to opening the scoring with the next attack, a short corner catching Sunderland off guard and allowing Stephen Gleeson to fire in a shot from the edge of the box that whistled just wide of Keiren Westwood's upright.
MK Dons were starting to threaten on a more regular basis and only a smart clearance from Matt Kilgallon stopped former Leeds team-mate Alan Smith making contact with Daniel Powell's drilled cross.
Cattermole received his marching orders on 32 minutes after referee Stuart Attwell adjudged that the midfielder had lunged into a challenge with young full-back Chicksen following a heavy touch from the Black Cats' skipper as he tried to lead a counter-attack for the visitors.
Powell had a chance to make the numerical advantage count for the hosts when he skipped past makeshift centre-back David Meyler but chose to pick out a pass when he appeared to have a clear run on Westwood's goal.
With the first half drawing to a close Dean Bowditch, fresh from his hat-trick against Bury at the weekend, came close to opening the scoring for MK Dons but could not bend his shot inside Westwood's far post.
MK Dons started the second half in a lively fashion and saw Darren Potter force Westwood to tip his long-range effort behind for a corner.
But Sunderland were ahead after 53 minutes when a free-kick was awarded to the visitors following Anthony Kay's bodycheck on McClean.
Gardner struck the ball perfectly and found the top corner of McLoughlin's net with the goalkeeper left motionless on his line.
Powell curled an effort inches wide before McClean's flashed a free-kick just past the post at the other end.
Karl Robinson introduced Charlie MacDonald and Ryan Lowe from the bench to give his side some fresh impetus and Lowe had a good chance only a couple of minutes after entering the fray as he found space inside the Sunderland penalty area but fired wide when well placed.
A number of Sunderland players started to look a little jaded with the game reaching its climax and MacDonald almost capitalised when he darted to the near post to meet Bowditch's pass - but shot wide from close range.
The game was then wrapped up when McClean eluded several challenges to find space inside the MK Dons' penalty area and fire low past McLoughlin.
O'Neill introduced winger Adam Johnson late on with the winger looking for match sharpness as he returns from a thigh injury.
The second goal seemed to take the edge off of MK Dons' performance, although MacDonald and Chicksen both had chances to score what would have been a thoroughly deserved consolation.