Oldham's recent run had lifted them into the League One play-off places but they were condemned to defeat by two-goal Izale McLeod.
The Dons had won only once away from home all season but they stayed solid in defence after hitting back to lead at half-time.
Off-colour Oldham did little to trouble the visitors with Luke Beckett's 16th goal of the season coming from a hotly disputed penalty.
Beckett almost broke through on six minutes but his volley was superbly kept out by Dons keeper Matt Baker diving to his left.
Dave Partridge headed over for Danny Wilson's strugglers and Oldham took the lead after 27 minutes as Chris Taylor controlled a loose ball on the edge of the box. The teenage winger knocked the ball past Aaron Wilbraham and was brought down as he tried to burst clear.
MK Dons insisted the foul had occurred outside their penalty area but their appeals were in vain as Beckett stepped up to send Baker the wrong way from the spot.
The visitors almost levelled within three minutes as McLeod led a counter attack and was foiled by Oldham keeper Lee Grant.
But McLeod would not be denied again as he picked up a stray back pass from Paul Edwards and used acres of time and space to drill his shot out of Grant's reach from 14 yards.
The in-form hit man struck again less than two minutes later following a long ball out of defence which caught Oldham flat-footed. He advanced on the keeper and found the bottom right hand corner from deep inside the box.
Paul Warne headed wide for Oldham and Beckett blazed over the top but Dons substitute Clive Platt was only denied by a goal line clearance from Latics midfielder Mark Hughes.
McLeod was unlucky not to complete his hat-trick with four minutes left on the clock as he out-paced Terrell Forbes down the right, cut inside and lashed a shot which had the crossbar rattling and keeper Grant completely stranded.