Oldham edged Portsmouth 1-0 in a fiery Fratton Park contest which saw both sides end the match with 10 men.
Jonathan Grounds' goal after 59 minutes was enough to hand the Latics all three points, before Portsmouth's Jordan Obita and Oldham's Cliff Byrne both saw red for violent conduct four minutes later.
Neither side created many clear-cut chances in a lacklustre first half, but the Latics should have gone ahead in a goalmouth scramble after 41 minutes.
Lee Croft's corner was met by Jean-Yves M'voto, whose header was well saved by Mikkel Andersen. Byrne lashed the rebound goalwards but was denied by a superb clearance on the line by Mustapha Dumbuya, who took a heavy knock in the process.
Oldham nearly took charge after 53 minutes when Dean Furman sent Cristian Montano racing through on goal but his shot across Andersen bounced back off the post.
The visitors finally went ahead when a wicked Grounds cross from the left evaded the Pompey backline and went into the net.
Both sides were then reduced to 10 men when Obita was dismissed for violent conduct by referee Carl Berry, before Byrne immediately followed.