Southend climbed above Oldham with a well-earned victory courtesy of goals from James Lawson and Mark Gower.
Teenager Lawson struck after just 10 minutes of his debut, heading in Mitchell Cole's cross from six yards.
Shaun Goater hit the crossbar before Gower made it two on the stroke of half-time, heading another Cole cross beyond Latics goalkeeper Chris Day.
Oldham had their chances but could only manage a consolation goal from Mark Banner's powerful driven effort.
Southend: Flahavan, Hunt, Barrett, Edwards, Wilson, Gower, Maher, Guttridge, Cole (Smith 77), Lawson (Bentley 70), Goater (Prior 88).
Subs Not Used: Griemink, Jupp.
Goals: Lawson 11, Gower 45.
Oldham: Day, Forbes, Bonner (Butcher 84), Owen, Scott, Tierney, Wellens, Edwards (Eyres 67), Killen, Liddell, Warne (Porter 67).
Subs Not Used: Poke, Hughes.
Goals: Bonner 69.
Ref: N Miller (Durham).