Karl Robinson's side moved to within six points of the play-off places after completing a quickfire double over the Latics, who they beat by the same scoreline at stadium:mk just days 10 earlier.
George Baldock gave the Dons a flying start in the fourth minute, drilling into the bottom corner from 20 yards for his first league goal.
Antony Kay's header was cleared off the line by Oldham defender Connor Brown, but Dons doubled their lead after 41 minutes as Izale McLeod raced on to Stephen Gleeson's through-ball and calmly slotted in from 14 yards.
It could have been three before the break but Ben Reeves saw his shot tipped on to the post by home goalkeeper Mark Oxley.
Oldham, having made a triple substitution, improved dramatically in the second half and grabbed a lifeline after 57 minutes when Charlie MacDonald converted a close-range header from Gary Harkins' corner.
Dons substitute Ryan Hall wasted a good chance, but the visitors were grateful to goalkeeper David Martin for a crucial late save to deny MacDonald.