Lee Hughes scored his third goal in two games to beat Crewe and send Oldham into the FA Cup third round.
He slammed home the winner four minutes before the interval, scoring from six yards after Mark Allott's cross.
Crewe had a glorious chance after only 17 seconds when a mistake by Dutch defender Stefan Stam let in Ryan Lowe, but he shot harmlessly wide.
Oldham dominated totally, with Crewe keeper Ben Williams kept busy, but they had to settle for a narrow victory.
Oldham: Crossley, Eardley, Hazell, Stam, Taylor, Allott,
Kilkenny, McDonald, Smalley, Hughes, Davies.
Subs Not Used: Bell, Kalala, Wolfenden, Lomax, Thompson.
Goals: Hughes 41.
Crewe: Williams, Woodards, Jones, McCready, Matthew Bailey,
Rix, Roberts (Bennett 73), Cox, Moore (Baseya 79),
Lowe (Maynard 46), Church.
Subs Not Used: Tomlinson, O'Connor.
Ref: Jon Moss (W Yorkshire).