Mike Petrasso's debut goal clinched Oldham a deserved 1-0 victory at Gillingham.
The 18-year-old Canadian, who joined the Latics on loan from Ipswich on Friday, looped a header over Stuart Nelson in the 57th minute after the Gills defence had failed to clear Danny Philliskirk's initial effort.
It was only the visitors' second away league win of the season and the first since their opening-day triumph at Stevenage.
But it was no more than they deserved, having had the best of the chances throughout.
Philliskirk should have put the Latics ahead after three minutes, but headed at straight at Nelson.
Joseph Mills also flashed a low curling effort just past the post and captain Korey Smith came close with a powerful 25-yard volley.
Gillingham - dumped out of the FA Cup at the hands of non-league Brackley on Monday - went closest to an equaliser through Cody McDonald, but the striker tamely shot at Mark Oxley after dispossessing Jonathan Grounds 20 minutes from time.
The visitors ended the game with 10 men after defender Genseric Kasunga was sent off five minutes from time for tangling with Danny Kedwell, which led to a mass brawl between the two teams.