Gillingham threw away a two goal lead as they started the season with a heavy defeat.
Cody McDonald put the Gills ahead early and Danny Kedwell doubled the lead from the penalty spot.
But MK Dons halved the deficit just before the break, with an own-goal from Kortney Hause and further goals from Will Grigg, Kyle McFadzean and another OG turned the game on its head.
A game that had started so well ended miserably for the Gills and a serious looking injury to McDonald made it a bad opening day for Peter Taylor’s side.
Gillingham – captained by Doug Loft - spent much of the first half defending, with all but McDonald getting behind the ball.
It was a ploy that started well. Twice McDonald broke clear of the defence to twice produce goals for the Gills – the second coming from Kedwell’s penalty.
McDonald, who hadn’t scored in pre-season, took just over six minutes to silence the doubters, wriggling free from centre-back McFadzean before tucking the ball away past keeper David Martin.
The hosts were rattled but kept pressing. Delli Alli lobbed a shot narrowly over and Gills keeper Stuart Nelson was out smartly to deny Dean Bowditch, after Ben Reeves had threaded a ball through the defence.
McDonald once again got the better of the MK defence to inflict more damage, this time beating Antony Kay to the ball, after John Egan had played a ball through. Keeper Martin came out and took McDonald down in the box.
Referee Tim Robinson showed the home keeper leniency by handing out a yellow card, when it could have been red. Kedwell rolled home from the spot to double Gills’ lead.
Nelson made a save at full stretch to deny Will Grigg but moments later was picking the ball out of his net.
From a corner Nelson could only get a touch on the ball, sending it in the direction of Hause, who inadvertently scored an own-goal with the back of his head.
A switch at the break saw Nelson replaced by back-up keeper Glenn Morris. Gillingham were forced into a second substation just five minutes into the second half, with McDonald injured in a challenge with Kay.
Morris showed what a quality back-up he is with a great save to deny Alli, after Ben Reeves’ ball split the Gills defence apart.
Three goals in a six minute spell turned the game on its head.
Danny Green delivered two killer crosses to put MK Dons ahead. His first, on 67 minutes, was headed home by Will Grigg and three minutes later McFadzean nodded in a third.
It got worse for the Gills on 73 minutes. A Green corner was whipped in and a deflection from Aaron Morris took it past Glenn Morris in the Gills goal.
Gillingham: Nelson (G Morris 46mins), Martin, Egan, Hause, Legge, Loft, Hessenthaler (Dickenson 77mins), Kedwell, McDonald (German 53mins), McGlashan, A Morris. Subs: Norris, Davies, Hare, Dack.
MK Dons: Martin, Hodson, Lewington, McFadzean, Kay, Green, Potter, Bowditch (Powell 83mins), Reeves (Hitchcock 86mins), Grigg (Afobe 76mins), Alli. Subs: McLoughlin, Flanagan, Randall, Powell, Baldock.