Latics fell to defeat at Boundary Park, as Halifax Town took the points with a second-half goal.
The away side dominated the opening 15 minutes, creating a number of chances which threatened the Latics goal.
Halifax’s attacking activity calmed down for the rest of the second-half, but Latics still failed to create anything more than half-chances.
Mike Fondop was sent-off as the game approached the one-hour mark, for an off the ball incident, and Latics were down to 10-men.
Magnus Norman denied Max Wright’s superb effort from inside the box, to keep the score level, moments before the referee awarded Halifax a penalty, as Josef Yarney was judged to have handled the ball in the area.
Former Latic Emmanuel Dieseruvwe took the penalty, which Norman saved, just for the 27-year-old to fire home the rebound, giving Chris Millington’s side the lead.
John Rooney and Timmy Abraham were substituted on, looking to give Oldham more attacking threat follow Fondop’s premature departure.
Abraham soon went into the referee’s book for winning a 50/50 against Harvey Gilmour in Halifax’s half.
Rooney fired in a corner-kick which saw Yarney dragged down inside the box, but the referee waved play on.
Alex Reid was substituted towards the end, in the final roll of the dice, but it was to no avail.
Oldham: Norman, J. Clarke, Hogan, Sheron, Shelton, Tollitt (Abraham 63), Fondop, Kitching, Chapman (Rooney, 70), Yarney, Nuttall.
Attendance: 7,459 (566)