Nile Ranger opened the scoring for the Shrimpers in the first half whilst substitute Jermaine McGlashen added the second 15 minutes from time to win the game.
Manager Stephen Robinson elected to stick with the same side which started Tuesday night’s game against Walsall.
Southend United midfielder Stephen McLaughlin had the first chance of the half, striking over the crossbar from 25 yards.
Mintues later and it was the turn of Oldham Athletic to go close as Billy Mckay turned on the edge of the box and forced a good save from Mark Oxley.
Athletic had shouts for a penalty on 12 minutes as Charles Dunne was pushed in the area but the referee was unmoved.
Southend United took the lead on 18 minutes through Ranger.
The striker controlled a corner into the box and acrobatically volleyed past Connor Ripley to give the Shrimpers the lead.
Latics looked for an instant response and won a corner straight from the restart. Ollie Banks delivered into the box but with the ball bobbling inside the area, Southend just managed to clear.
Robinson’s men were struggling to get going in the first half but were still looking a threat from set pieces.
After good work from Latics winger Ryan McLaughlin on the right, he won a corner which Banks took, but Peter Clarke could not latch onto the end of the set piece.
Southend were forced into a change before the break as Simon Cox was replaced by Marc Antoine-Fortune.
The visitors went into the break in front and that forced manager Robinson into a double switch at half time as Carl Winchester and Lee Croft came on.
The pair instantly combined on the edge of the box with Croft setting Banks up but the midfielder could not direct his volley on target.
Croft soon found his way into the book after pulling back Anthony Wordsworth but Latics continued to attack with Flynn the next man to go close.
Whilst his effort from 25 yards went wide, two minutes later Clarke’s free header from the penalty spot was tame and the goalkeeper saved.
Latics needed an injection of pace and almost found a leveller as Winchester’s strong run and shot cross was not attacked by an attacker.
With 20 minutes remaining, Winchester laid the ball into the path of Ladapo to strike from 18 yards but he hit his effort wide of the post.
Southend doubled their lead on 77 minutes after McGlashen punished an error in the middle of the park.
The winger nicked the ball off Banks, raced one-on-one with Ripley, and despite the goalkeeper’s best efforts to keep his shot out, he followed up and put the Shrimpers two goals ahead.
Ripley was forced into a late save as he tipped a Wordsworth free kick past the post whilst in the final minute of the game, Clarke hit the crossbar as Latics came away without any points.
Oldham Athletic: Ripley, Law, Burgess, Clarke, Dunne, Green (Winchester 46’), Banks, McLaughlin (Croft 46’), Flynn (Erwin 66’), Ladapo, Mckay.
Subs not used: Kettings, Wilson, Dummigan, Osei.
Southend Unied: Oxley, Wordsworth, Thompson, Timlin, Cox (Antoine-Fortune 35’), McLaughlin, Atkinson, Leonard, Demetriou, Ferdinand, Ranger (McGlashen 46’).
Subs not used: Smith, White, O’Neill, King, Matsuzaka.
Goals: Oldham Athletic 0-2 Southend United (Ranger 18’, McGlashen 77’)