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 home side saw Kyle McFadzean sent off before an injury-time handball gifted them a chance for a point.
Carl Baker sent the keeper the wrong way but 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.”