Sammie Szmodics started the game with a bang, scoring at the far post with less than two minutes on the clock.
It was 1-0 to the U's at the break, and that's how it stayed to give the U's three valuable points.
Ben Gordon dropped down to the bench, with Gavin Massey moving to the left to accommodate Hewitt.
Boss Tony Humes made one change to his starting line-up, bringing Elliott Hewitt back after a three match suspension.
The win brings the U's back to within one point of safety at the bottom of League One.
As in recent matches, the U’s were quickly out of the blocks but against Oldham, they made that early dominance count.
A second minute corner was cleared back out to the taker David Fox, who lofted his left foot effort high into the far post area.
Gavin Massey had got away from former U’s full back Brian Wilson and headed back into the danger area, where Sammie Szmodics pounced and sidefooted firmly into the bottom corner.
The goal stunned the home side and they failed to put together any meaningful attacks against the U’s, who were being well marshalled by skipper Fox.
The half was almost twenty minutes old before the next attack from either side materialised, with Elliott Hewitt’s dangerous cross headed behind by Wilson.
Two minutes later, the home side had their first effort, albeit a weak one, when Philliskirk headed well wide from a right wing corner.
On the half hour, Hewitt read a pass out of the Oldham defence and drove forward before hitting a tame shot goalwards that didn’t threaten Kean in the home goal.
Neither keeper was really being tested and the U’s next attack came and went without an effort on goal.
Fox nicked the ball just outside his own area, drove forward before picking out Szmodics on the left but the cross was too high and high and went out for a goal kick.
The U’s scorer then tried an audacious overhead kick form the edge of the penalty area, which went well wide on the target.
It was forty five minutes great work from the U’s but Tony Humes would have been demanding another from his side.
Oldham came out for the second half with renew vigour and an appetite to lift the tempo but the U’s matched them in the early stages.
Oldham had the first chance but Jones horribly snatched his shot and it went wide of Walker’s right hand post.
Gavin Massey latched onto a ball down the U’s left and after cutting inside, was denied by the lags of keeper Kean.
Kean then unconvincingly pushed away a Briggs shot and Hewitt was penalised as he challenged for the loose ball.
All these chances came in the first five minutes of the half and on fifty two minutes, Walker comfortably saved when a long range effort was deflected in front of him.
He had to work much harder three minutes later, when he dived full length to tip a Mellis curler round the post.
A long through ball gave the hosts their next chance but Walker was once again up to the challenge.
Alex Wynter got to the long ball first but his header back to his keeper lacked any pace and Forte was onto it, only to be denied by Walker staying strong and blocking the ball.
There was a let off for the U’s with ten to go, as Walker saved down to his right from a Kelly volley when the Oldham midfielder should have done much better.
Jack Marriott came on for the scorer Szmodics on eighty two minutes but had to watch from afar when the next chance of the game came.
A patient bit of passing from the home side ended with substitute Poleon shooting wide in the eighty second minute.
Macauley Bonne replaced Elliott Hewitt with a couple of minutes to go but it was the home team that was on the front foot in the final stages.
A shot from Philliskirk flew wide and then an offside flag ruined the home crowd’s celebrations in injury time when the ball did find the net.
The final whistle went seconds after that, and the U’s had reduced the gap between them and safety back to one point, with two home games to play in the next week.
MK Dons and Bristol City are the visitors to the Weston Homes Community Stadium though, so more determined performances will be needed to add valuable points to the total.