Full-back Robbie Williams sealed the points with a cunning free kick which condemned the Latics to back-to-back home defeats.
Huddersfield had the better of a wind-affected game and almost went ahead when top scorer Jordan Rhodes glanced against the bar from an Anthony Pilkington set piece.
Oldham had a lucky escape when Sean Gregan appeared to handle a Gary Roberts' cross, only for the referee to turn down penalty claims.
But Huddersfield broke through after 59 minutes. Williams lined-up his free kick to the left of goal and, with keeper Dean Brill expecting a cross, he instead smashed it inside the near post.
Rhodes went close to doubling the lead and Michael Collins also wasted a chance before Oldham created their best opening after 78 minutes. Ex-Huddersfield striker Pawel Abbott cut into the box and was denied by Alex Smithies before the rebound flew off target via substitute Nick Blackman.