A 70th-minute goal from substitute James Dayton was good enough to claim the three points for a Latics side now unbeaten in their last eight games.
It left Carlisle needing to win their last two away fixtures against Crawley and Wolves to have an outside hope of avoiding relegation.
Oldham played the neater football without creating many chances in a scrappy first half.
Carlisle’s lack of composure in their opponents’ box was evident although Gary Madine forced goalkeeper Paul Rachubka to back pedal and turn a spectacular 35-yard shot over the crossbar.
Then in first-half injury time, from a free-kick awarded when Adam Lockwood picked up a booking for bringing down David Amoo, James Berrett’s curler landed on the top of the Oldham crossbar.
Latics’ substitute Joel Byrom thought he had scored with a header midway through the second half from James Wesolowski’s right-wing cross, but he was flagged narrowly offside.
But Oldham went ahead soon after when another of their second-half substitutes, Dayton, took advantage of some weak tackling to cleverly work an opening and slip the ball past helpless Cumbrians goalkeeper Jordan Pickford from six yards.
Carlisle’s late revival was in vain as Rachubka denied Danny Redmond and David Symington with two brillant saves.