A low key start, with rain falling and the crowd (25,906) subdued, Oldham dominated the early stages led by Chris Taylor who went off with a leg injury on 18 minutes, to be replaced by Deane Smalley.
This seemed to wake up the crowd but the Latics looked like they wanted a goal and they got one in the 27th minute when Reuban Hazell volleyed in a right foot shot from 25 yards, 0-1.
Oldham continued to press and seemed better than Leeds in every department. This was illustrated when Leeds had to defend a corner on 36 minutes and failed to prevent Neal Trotman heading in from 12 yards, 0-2.
The nightmare continued when a cross from Oldham's Craig Davies was deflected into the net by Leeds midfielder, Andy Hughes, 0-3.
At the start of the second half Leeds brought on strikers Leon Constantine for Radostin Kishishev and Tore Andre Flo for Seb Carole and within seconds of the re-start, Constantine, with his first touch of the ball, converted a cross from Jermaine Beckford at close range, 1-3.
Ben Parker came on for the injured Alan Thompson on 55 minutes.
Oldham held their game and withstood pressure from the powerful Leeds strike force. A goal by Tresor Kandol was ruled offside but nothing United did could make up the first half deficit and they went down to their first home defeat of the season.
It is truly turning out to be a dreadful Christmas period for the whites.
Leeds United 1 Oldham Athletic 3