Latics conceded twice in both halves to suffer defeat in the final away fixture of the campaign against Mansfield Town.
Zak Dearnley marked his return from injury with a second-half goal but it proved to be no more than a consolation on a hugely disappointing afternoon at Field Mill.
Latics went behind inside the opening 12 minutes and the game was one-way traffic in favour of the home side for the most part, with the visitors unable to make a meaningful impression as an attacking entity.
Keith Curle made three changes from match against Grimsby Town last weekend, Dearnley returning after a 22-game absence, while Marcus Barnes and Ben Garrity also started.
The home side were quick out of the blocks with chances in the opening minutes for Tyrese Sinclair and George Lapslie.
They took the lead through Sinclair, who dispatched an angled finish over Laurie Walker after George Maris won possession in midfield before releasing Jamie Reid to play in the striker.
Conor McAleny tried to free Dearnley in behind the home defence as Latics looked to respond but it was Mansfield who continued to control the play.
Sinclair shot over after a good turn on the edge of the box and minutes later he fed the ball into Keaton Ward but he was unable to finish.
Walker made a save from Lapslie after Latics failed to clear a corner from Stephen Quinn but the dangerous midfielder was on target seven minutes before the break, getting the final touch after an initial effort from Stephen McLaughlin.
Latics got themselves a lifeline six minutes after the re-start, Dearnley profiting on a breakdown in communications between goalkeeper Aidan Stone and Ryan Sweeney to score from close range.
For a brief period, the goal appeared to lift Latics’ performance, Carl Piergianni heading over from a Nicky Adams free-kick. Harry Clarke also went close after meeting a corner from Callum Whelan.
But the respite for the visitors was only brief, Walker denying Reid after good approach work from Quinn.
The home side restored their two-goal advantage with ten minutes remaining, Lapslie adding his second at the far post to convert a right-wing cross from Maris.
And after Walker had saved from Harry Charsley, Mansfied scored a late fourth, Reid converting the rebound after James Clarke cut in from the right before his initial shot was saved.
Oldham Athletic: Walker, Clarke, Jameson, Piergianni, Borthwick-Jackson, Adams (Fage 70), Whelan, Garrity, McAleny (Bahamboula 51), Dearnley (Keillor-Dunn 51), Barnes (McCalmont 60).
Subs not used: Bilboe, Badan, Vaughan.
Mansfield Town: Stone, Gordon (J Clarke 73), Perch, Sweeney, McLaughlin, Maris, Ward (Bowery 73), Quinn (Charles 82), Lapslie (Charsley 82), Sinclair (Law 82), Reid.
Subs not used: Pardington, Wright.
Referee: Anthony Coggins