Jonathan Grounds hit a 73rd-minute winner to give Oldham a deserved 1-0 victory over Swindon at the County Ground.
The left wing-back finished off a neat move initiated by the influential Gary Harkins. He set up substitute Jon Stead, who joined the Latics in a last-minute January transfer window move, but his shot was blocked and Grounds fired home the rebound.
It was Oldham's first away win since late November and dented the play-off hopes of out-of-sorts Swindon, who finished the match with 10 men after half-time sub Troy Archibald-Henville was dismissed late on for a second yellow card offence.
Oldham deserved their success. Their work rate was superior to that of the Robins in a scrappy affair played on a heavy surface and in wild, windy conditions.
Chances were at a premium throughout, with goalkeeper Mark Oxley saving Swindon's solitary first-half effort from a Ryan Harley free-kick.
Stead almost put the Latics in front from a header which Wes Fotheringham turned over the crossbar, but 17 minutes from time he played a part in the visitors' winning goal.