John Sheridan had collected the award for November and his side had won their previous five league games but they never looked like adding to that as Chesterfield outplayed them from start to finish.
Two goals from Colin Larkin put the home side on top and although Neal Eardley replied with a free-kick, the visitors never looked like turning the game around.
Sheridan must have been surprised at how easily his in-form side were made to look so poor by a Chesterfield team that buzzed eagerly all over the field.
Kevan Hurst was a constant threat on the Chesterfield left while the pace of Larkin exposed the Oldham defence.
But it was in central midfield where Oldham struggled as Derek Niven and Mark Allott ran the show.
Allott was outstanding against his former club, although some of the gloss was taken off his afternoon when he picked up a fifth booking and a suspension in the second half.
Oldham's Richie Wellens will also serve a ban after he was yellow carded near the end but the playmaker was a peripheral figure alongside many of his team-mates.
Chesterfield could have won by a bigger margin but the result showed just how little there is between the teams in this division.
Oldham were always struggling after Larkin headed in at the back post in the 14th minute when Hurst crossed from the left and then Paul Shaw sent him through to place a low shot into the bottom right hand corner.
Oldham did not look like responding until they won a free-kick in first-half stoppage time and Eardley found a way round the defensive wall with a right-foot shot that found the net via the fingers of Barry Roche.
That should have inspired the visitors but, although they started the second half with greater purpose, the chances did not come.
Instead it was Chesterfield who threatened to add to their tally and Shaw should have scored at least once.
He was denied by Les Pogliacomi in the 63rd minute after Larkin had set him up and then he somehow failed to find the net from three yards after another goalmouth scramble.
Hurst continued to torment the visitors and was close to scoring when his curling shot in the 83rd minute forced Pogliacomi into another diving save.