Match ends, MK Dons 1, Brighton and Hove Albion 2.
MK Dons missed an injury-time penalty as they were beaten by Brighton, who climbed to second in the table.
Two goals in six minutes by substitute Tomer Hemed looked to have sealed the points for Brighton before Anthony Kay headed one back for the home side.
The hosts had defender Kyle McFadzean sent off before an injury-time handball gifted them a chance for a point.
Midfielder Carl Baker sent his spot-kick went wide, and the Dons drop into the bottom three.
The Dons started brightly but ran out of steam before half-time, after which the visitors - who moved four points behind leaders Burnley - took control.
Within minutes of coming on for former Dons favourite Sam Baldock, Hemed had the ball in the net twice in quick succession - first from the penalty spot and the second a free header.
Kay gave his side hope, but having been booked for an altercation after that goal, McFadzean then received a straight red after elbowing Hemed, seemingly ending any chance of a comeback.
Baker's late failure from the spot cost the Dons a draw and saw them slip below Rotherham, who won at Ipswich.
MK Dons boss Karl Robinson: "I thought we were very good - our energy and desire against one of the best teams in the division was there for all to see.
"They've won the lottery here today, but I've got so much respect for them but for us to be missing so many players and still compete was pleasing.
"We've got to get out of the position we're in, it's as simple as that.
"But there's a tremendous sense of pride for everyone leaving the stadium today, because we've pushed them all the way and they've given all they can."
Brighton assistant manager Colin Calderwood: "Fortunately for us Hemed has come on and has had a terrific impact on the game. Obviously his goal tally for us speaks for itself, it's increasing and that's good for us because it becomes a good focal point.
"But we can't forget the impact Sam Baldock has had on the team too because he is the catalyst for a lot of what we do.
"Of course we are going to argue about the decision for the penalty kick too, because none of the boys inside think it was a penalty - it's actually hit one of our lads in the face.
"But at least it ended up nice for us and it was perhaps and little bit too exciting from our point of view."
- 5McFadzeanBooked at 71mins
- 23WilliamsSubstituted forBakerat 76'minutes
- 17PowellSubstituted forSpenceat 76'minutes
- 38HallSubstituted forRevellat 61'minutes
- 13StockdaleBooked at 70mins
- 2BrunoBooked at 69mins
- 23RoseniorBooked at 90mins
- 38SkalakBooked at 29minsSubstituted forSidwellat 77'minutes
- 7KayalBooked at 82mins
- 6StephensBooked at 61mins
- 21WilsonSubstituted forLua Luaat 78'minutesBooked at 90mins
- 9BaldockSubstituted forHemedat 52'minutes
- 30Lua Lua
- Chris Kavanagh
- Shots on Target
Second Half ends, MK Dons 1, Brighton and Hove Albion 2.
Attempt missed. Alex Revell (MK Dons) header from the centre of the box is close, but misses the top left corner. Assisted by Dean Lewington with a cross.
Offside, Brighton and Hove Albion. Liam Rosenior tries a through ball, but Kazenga Lua Lua is caught offside.
Foul by Kazenga Lua Lua (Brighton and Hove Albion).
George Baldock (MK Dons) wins a free kick in the defensive half.
Foul by Connor Goldson (Brighton and Hove Albion).
Nicky Maynard (MK Dons) wins a free kick in the attacking half.
Kazenga Lua Lua (Brighton and Hove Albion) wins a free kick in the defensive half.
Foul by Darren Potter (MK Dons).
Penalty missed! Bad penalty by Carl Baker (MK Dons) right footed shot is close, but misses to the left. Carl Baker should be disappointed.
Kazenga Lua Lua (Brighton and Hove Albion) is shown the yellow card.
Liam Rosenior (Brighton and Hove Albion) is shown the yellow card.
Penalty conceded by Dale Stephens (Brighton and Hove Albion) with a hand ball in the penalty area.
Corner, MK Dons. Conceded by Liam Rosenior.
Offside, Brighton and Hove Albion. Beram Kayal tries a through ball, but Tomer Hemed is caught offside.
Attempt saved. Beram Kayal (Brighton and Hove Albion) right footed shot from outside the box is saved in the bottom left corner. Assisted by Jamie Murphy.
Foul by Beram Kayal (Brighton and Hove Albion).
Carl Baker (MK Dons) wins a free kick in the defensive half.
Beram Kayal (Brighton and Hove Albion) is shown the yellow card.