Oldham preserved their unbeaten away record and ended Chesterfield's formidable home run to claim their first win in nine matches after carving out a 1-0 victory.
Centre-half Fitz Hall headed a David Eyres free-kick over Andy Richmond in the 22nd minute to settle a game that was dominated by referee Joe Ross.
The London official angered both managers and sets of players with a succession of baffling decisions and booked four players in the first 20 minutes.
But Oldham kept their shape to deny an off-key Chesterfield a way back in to a match that was never allowed to flow.
Hall's header was the first league goal Chesterfield had conceded at home for 742 minutes, although there should have been more for the visitors but Wayne Andrews wasted several great chances.
Chesterfield had their moments after the break with Mark Allott firing over, but Oldham kept the home side at arms length and are still the only club in the country unbeaten away from home.