Match ends, MK Dons 1, Chesterfield 2.
Caolan Lavery scored a last-minute winner against 10-man MK Dons to move Chesterfield to within one point of the League One play-off places.
Chesterfield's Gary Roberts fired against the post before on-loan Chelsea midfielder Lewis Baker sent a curling shot into the top right corner.
Roberts coolly levelled and Dons were soon a man down following Dean Lewington's second yellow.
Spireites keeper Tommy Lee denied Carl Baker before Lavery won it.
The on-loan Sheffield Wednesday forward was first to meet a Tendayi Darikwa cross and beat Ian McLoughlin with a flicked shot.
Defeat sees Karl Robinson's Dons slip to third, a point behind Preston North End, who moved up to second with a draw against Doncaster Rovers.
MK Dons boss Karl Robinson told BBC Three Counties Radio:
"We know we weren't good enough, all of us. I have to take responsibility for it, it's my team, it's the team I put out and we didn't perform well at all.
"The goals tonight were ridiculously poor.
"I didn't see our style tonight and we have to find that bravery on the ball again.
"I have to be the man to come and apologise in front of our fans - I'm sorry."
- 12SpenceBooked at 26minsSubstituted forHodsonat 72'minutes
- 3LewingtonBooked at 80mins
- 34BakerSubstituted forAndrewsat 84'minutes
- 35WilliamsSubstituted forBakerat 36'minutes
- 5MorsyBooked at 24mins
- 11RobertsBooked at 16minsSubstituted forDieseruvweat 90+4'minutes
- 24BanksSubstituted forAriyibiat 62'minutes
- 13LaverySubstituted forHarrisonat 90+4'minutes
- Chris Sarginson
- Shots on Target
Second Half ends, MK Dons 1, Chesterfield 2.
Substitution, Chesterfield. Byron Harrison replaces Caolan Lavery.
Substitution, Chesterfield. Emmanuel Dieseruvwe replaces Gary Roberts.
Gary Roberts (Chesterfield) wins a free kick in the defensive half.
Foul by Keith Andrews (MK Dons).
Goal! MK Dons 1, Chesterfield 2. Caolan Lavery (Chesterfield) right footed shot from very close range to the bottom left corner. Assisted by Tendayi Darikwa.
Corner, Chesterfield. Conceded by Kyle McFadzean.
Attempt missed. Caolan Lavery (Chesterfield) header from the centre of the box is close, but misses to the left following a corner.
Corner, Chesterfield. Conceded by Antony Kay.
Attempt blocked. Sam Morsy (Chesterfield) right footed shot from outside the box is blocked.
William Grigg (MK Dons) wins a free kick on the right wing.
Foul by Ian Evatt (Chesterfield).
Substitution, MK Dons. Keith Andrews replaces Lewis Baker.
Attempt blocked. Sam Morsy (Chesterfield) right footed shot from the right side of the box is blocked.
Attempt saved. Carl Baker (MK Dons) left footed shot from the right side of the box is saved in the top left corner.
Second yellow card to Dean Lewington (MK Dons).
Foul by Dean Lewington (MK Dons).
Jay O'Shea (Chesterfield) wins a free kick in the defensive half.
Antony Kay (MK Dons) wins a free kick in the attacking half.