Chris Taylor and Mark Allott condemned Orient to their fifth consecutive defeat and prompted visiting manager Martin Ling to launch an attack on his players.
A furious Ling blasted: "It was terrible, unacceptable and the players have been told in no uncertain terms that the first 45 minutes in particular were not something I want to be associated with.
"We were rubbish. Some of them are playing as though they have their swim shorts and flip-flops on ready for summer, but they won't be here next season if they keep performing like that."
Orient were always on the back foot as Oldham, who were ravaged by injuries, belied their inexperience.
Allott was the first to go close and they took a deserved lead midway through the first half after captain Sean Gregan set them on their way.
His pass down the right was chased by teenage striker Deane Smalley, who showed excellent pace before passing inside to Taylor.
Taylor picked his spot with a low drive into the bottom corner from 20 yards for his fifth goal of the campaign.
Oldham had chances to quickly double their lead as Matt Wolfenden headed at keeper Glenn Morris and also flicked inches off target from Taylor's cross.
Adam Boyd wasted a rare opening for the visitors but Morris had to dive full length to thwart Neal Eardley.
Oldham's second arrived three minutes before the break as Orient failed to clear a set-piece and Allott stepped up to smash an unstoppable first-time drive high into the net from just outside the box.
It could have been three in the 55th minute as Smalley was only just unable to convert from close range following a mazy run by the dangerous Taylor.
Orient improved in the last half- our but they could make little impression going forward and the nearest they came to scoring was when Jason Demetriou hit a curling shot beyond the far post.