Cheltenham Town cruised into a 2-0 first-half lead with some slick football up until the break. However, Oldham stormed back in the second half and denied the Robins their first crack at the second round since 2005.
Cheltenham made the perfect start with a goal after only five minutes. A throw-in from wide on the left found its way to Darren Kenton in the penalty area and he laid it back for Scott Murray to lash in from 18 yards out.
Play ebbed and flowed from end to end with Lewis Alessandra the main threat for Oldham. He forced Cheltenham goalkeeper Shane Higgs into a good save then ran onto a long pass leaving defender Drissa Diallo in his wake, but despite taking the ball around Higgs, it ran away from him down the hill and the teenager was unable to finish.
Cheltenham finished the first half as they had started it with Lloyd Owusu blazing over from 15 yards then Murray getting up to meet a cross from Owusu with a textbook downward header.
The ball deflected off striker Paul Connor and almost crept inside Mark Crossley's right-hand post but the goalkeeper flew across to save acrobatically.
Cheltenham did extend their lead a minute before half-time, however. Owusu challenged for a free-kick taken by Diallo but was dragged to the ground by Oldham captain Sean Gregan.
Referee Phil Gibbs pointed to the spot and Owusu scored with a low shot beyond Crossley's reach.
The second half was a much tighter affair with fewer chances for both sides, although Oldham dragged themselves back into the contest only four minutes after the re-start, when Deane Smalley was impeded by Lewis Montrose when trying to reach a Danny Whitaker corner.
Chris Taylor's spot-kick was brilliantly saved by Higgs but Taylor followed up to net the rebound.
Murray volleyed just wide for Cheltenham not long afterwards but Oldham were doing most of the attacking in the second half and levelled the scores 14 minutes from time, when substitute Kevin Maher found Whitaker on the edge of the box and his shot took a heavy deflection on its way in.
Cheltenham could have won it late on when Owusu met a long throw from Lee Ridley with a volley against the post.
Owusu then latched onto a header from Damian Spencer, but Crossley saved smartly with his legs, taking the tie back to Boundary Park where Oldham have already beaten Cheltenham 4-0 this season.