John Sheridan's unbeaten side have won five of their first six games and earned this latest maximum haul with goals from Lee Hughes and Mark Allott.
It was a gripping encounter at Boundary Park as both teams played attacking football and did enough to suggest they can maintain bids for promotion.
The two goalkeepers were outstanding, with Willy Gueret making a pair of brilliant saves to keep MK Dons in the game and Oldham's Mark Crossley keeping out Mark Wright's first-half penalty.
Top of the table Oldham made the perfect start as Hughes, back in the line-up after a groin injury, scored his fourth goal of the season.
He chased a pass from Andy Liddell down the right flank and superbly lobbed in from the corner of the box as Gueret dashed off his line.
Oldham had a chance to double their lead through Lewis Alessandra but the visitors were awarded their spot-kick on the quarter-hour mark when Shaun Cummings crossed from the right and the ball bounced against Sean Gregan's hand.
Oldham were unhappy with the decision, only for Crossley to rescue them as he reached Wright's penalty at the bottom of his right-hand post.
The Dons were a threat and they had Sam Baldock's effort ruled out for offside before Aaron Wilbraham squandered a clear chance.
The second half was even and entertaining but Gueret was the star as he denied both Alessandra and Hughes with brilliant stops.
Crossley saved from Wilbraham at the other end and Oldham sealed victory deep into stoppage time.
Chris Taylor found space down the left and picked out Allott, whose low 20-yard drive flew into the bottom corner of the net.