Robins’ top scorer Aaron Wilbraham netted his 18th goal of the season, but Oldham deservedly hit back through highly-rated midfielder Carl Winchester.
City made the brighter start and Wilbraham headed inches wide from Korey Smith’s far-post cross.
Joe Bryan’s header forced a reflex save from Oldham keeper Joel Coleman, but at the other end Frank Fielding made a scrambling stop when Mike Jones let fly from 20 yards.
Fielding dived full length to palm out a long-range effort from Connor Brown, but the visitors went ahead after 71 minutes when Luke Freeman sent in a left-wing cross which Wilbraham slid home from six yards.
Oldham, though, levelled just four minutes later as Winchester turned into space 25 yards from goal and unleashed a powerful drive into the bottom corner.
The Latics almost snatched a winner, but Fielding made a superb save from Conor Wilkinson before charging off his line to deny Jonathan Forte.