Mike Jones' excellent free kick just before the half time break gave Dean Holden his first win as temporary boss.
The midfielder struck on the 42nd minute to ensure Latics came away from Vale Park with all three points.
Latics welcomed Adam Lockwood back into the starting 11 for his first competitive start since the last game of the season against Notts County.
It was the visitors that started the game the more livelier of the two.
Jonathan Forte, Danny Philliskirk and Dominic Poleon were full of energy as they searched for an early goal. Forte almost bulldozed his way through five minutes into the game but Chris Neal collected the ball well.
Philliskirk was next to go close for Latics on ten minutes. The forward found space inside the penalty area but dragged his shot wide into the side netting.
Forte should have opened the scoring two minutes later but failed to convert from six yards.
Carl Winchester played the ball to Poleon on the right and he crossed for Forte who somehow missed the target from deep inside the box.
Athletic continued their domination of the opening 20 minutes with Winchester playing an integral part in Latics' forward play.
The Valiants started to apply some pressure to Jake Kean's goal and striker Ben Williamson should have converted his header from inside the box when presented with a clear-cut chance.
Vale's number 20, Mark Marshalll, was proving a constant threat on the right-hand side but Lockwood and James Wilson dealt well with the balls into the box.
Jones almost opened the scoring on 38 minutes but curled his effort wide of the post after being set up by Forte.
The midfielder did not let that affect him and he gave Athletic the lead on 42 minutes.
The 27-year-old shaped up a free kick from all of 30 yards and blasted the ball beyond the goalkeeper into the bottom corner to give Latics the lead going into the half time break.
The goal the midfielder's fifth strike of the season, all coming from outside the box.
Vale upped the tempo following the start of the second half, causing a succession of corners but Kean was out to collect each ball.
Latics nearly extended their lead ten minutes after the break through an unlikely source.
Jones played the ball wide for the defender who cut inside and powered a shot goalwards but Chris Neal tipped the ball over the crossbar.
On the hour mark, Latics defended resolutely as Vale continued their onslaught on the Athletic goal.
First of all, Kean pulled off a world class save to deny Pope from six yards and from the resulting corner, Brown was forced to head off the line after the forward headed goalwards.
Latics were under intense pressure and Marshall had the opportunity to pull a goal back but missed his kick and the chance passed.
Vale were forcing themselves upon Latics but the defence stood resolutely with Kean a commanding force between the sticks.
Conor Wilkinson returned to the action on 75 minutes, replacing Poleon and made an immediate impact, comfortably holding the ball and bringing others into play.
Latics defended from the front in the final ten minutes and almost extended their lead on 85 minutes.
Wilkinson fed the onrushing Philliskirk who raced one-on-one with Neal only to be denied by the goalkeeper.
It was backs against the walls stuff heading into the five minutes of additional time but Latics held on to gain the valuable three points to continue their play-off push.
Port Vale: Neal, Dickinson, Robertson (Dodds 81'), Williamson, Pope, O'Connor, Brown (Lines 64'), Moore, Marshall (Daniel 64'), Veseli, Inniss.
Subs not used: Johnson, Yates, McGivern, Birchall.
Oldham Athletic: Kean, B.Wilson, J.Wilson, Lockwood, Brown, Kelly, Winchester (Dieng 85'), Jones, Philliskirk, Poleon (Wilkinson 75'), Forte.
Subs not used: Coleman, Kusunga, Truelove, Jacobs, Murphy.
Goals: Port Vale 0-1 Oldham Athletic (Jones 42')
Attendance: 4,423 (236 visiting supporters)