First-half goals from Paul Warne and Gary McDonald put the Latics in control and substitute Kayode Odejayi's late goal for Cheltenham was no more than a consolation.
The home side have now lost nine of their last tne league games and will have to show more of the fighting spirit they displayed in the second half if they are to stand any chance of avoiding the drop straight back to League Two.
Oldham took control of the first half with some neat and tidy passing with front two Warne and Chris Porter, plus Andy Liddell down the right, proving too much for a hesitant Robins backline.
Midfielder McDonald sent a free header over the bar and midfielder Chris Taylor saw an angled drive pushed wide by Cheltenham goalkeeper Shane Higgs during a bright opening by the visitors.
Cheltenham defender Shane Duff headed against the top of the bar from a Grant McCann corner, but the opening goal went Oldham's way and deservedly so on 23 minutes.
Porter and Taylor got up to meet a Simon Charlton cross from the left and when the ball fell to Warne on the edge of the box, the former Rotherham United man had time and space to volley past Higgs.
Oldham forced an amazing 15 corners during the first half, a measure of their domination, so it was really no surprise then their lead was extended four minutes from the break.
Right-back Kelvin Lomax crossed from wide on the right, Porter flicked it on and McDonald sent a looping header over the goalkeeper and inside the far post.
Cheltenham stepped up a gear in the second half with Oldham content to sit back and keep things tight.
Oldham goalkeeper Les Pogliacomi got down to save well from Brian Wilson and Gavin Caines and there was an amazing incident with five minutes to go.
Three Cheltenham players found themselves in front of goal with the offside flag down, but Damian Spencer elected to blast a shot that flew wide rather than play in a team mate in a better position.
The home side finally pulled one back in the last minute when Odejayi headed in a cross from Smith but it was too little, too late for the Robins.