MK Dons fell four points adrift of league leaders Lincoln City on Saturday as they lost their first league game at Stadium MK, going down 1-0 to Colchester United.
Luke Prosser's 12th minute goal was enough to win it for third placed Colchester, who closed the gap to Dons to just two points before Christmas.
The side remained unchanged from the one which was named, but never played last week in the rained off affair at Newport County. The big news though saw Chuks Aneke return to the substitutes bench after missing the the game against Carlisle.
Dons made a bright start, with both Kieran Agard and Conor McGrandles coming close, but it would be the away side who took the lead after 12 minutes. Captain Luke Prosser made a break to the near post to reach a low corner whipped in, and his deft flick saw it sail over Lee Nicholls' head and into the roof of the net.
The goal really knocked the stuffing out of what was an otherwise good start for the home side. From the quick passing attacking football they were playing prior to the opener, Dons were suddenly short of ideas and struggled to keep hold of the ball as the visitors gained the upper hand.
Gradually, Dons' confidence came back but Rene Gilmartin kept his powder dry. McGrandles was looking the best outlet for the home side, getting in behind the Colchester defence on countless occasions, but the final delivery was lacking. Rhys Healey shook off a shaky start too, and was inches away from testing Gilmartin from Dean Lewington's cross shortly before the break.
It would be his last involvement though as he was withdrawn at half time along with Kieran Agard as Chuks Aneke and Peter Pawlett came on to replace them.
The pair made a big impact on the way Dons were playing too, with Aneke first firing just over from 18 yards before Pawlett played a key role in the build-up to Gilmartin's first real save of the game, denying Ouss Cisse's neat strike from the edge of the box.
While the tide was fairly one-way for much of the second period, Sammie Szmodics was inches away from doubling Colchester's lead after he gambled on Brennan Dickenson's ball into the box, but couldn't quite get on the end of it.
Luke Norris too should have done better when the ball found him just inside the box with the whole goal to aim at, but he blasted over.
Osman Sow's introduction with 16 minutes to go added to Dons aerial threat, but when he headed wide late on, the writing was on the wall.
Referee: Chris Sarginson
MK Dons: Nicholls, Cargill, Houghton, Williams, McGrandles, Lewington, Gilbey, D'Ath, Cisse (Sow 74), Agard (Pawlett 46), Healey (Aneke 46)
Subs not used: Moore, Watson, Hancox, Simpson
Colchester United: Gilmartin, Jackson, Lapslie, Prosser, Kent, Pell, Norris (Mandron 86), Szmodics (Comley 90), Dickenson, Eastman, Nouble
Subs not used: Barnes, Senior, Wright, Gondoh, Kensdale
Booked: Pawlett, Laplsie, D'Ath, Gilbey, Lapslie