The Latics looked to be heading for their first win in five games after on-loan St Mirrren midfielder Gary Harkins struck shortly after half-time.
The visitors started brightly with Adam Lockwood directing a far-post header onto the roof of the net in the second minute. David Worrall also forced Crewe goalkeeper Ben Garratt into a near-post stop but there was a distinct lack of quality from both struggling sides and goalmouth action was sparse.
Joel Byrom, signed on loan from Preston this week, appeared to have more time than his finish suggested when blasting a deflected shot across the face of goal just before the interval.
Oldham made the breakthrough seven minutes after the restart when Harkins made the most of enterprising play from James Wesolowski and Johnson Clarke-Harris. He cut in from the left of the box to beat Garratt as his near post with a fierce right-foot shot
Clarke-Harris twice went close to adding to the tally in the space of a couple of minutes. Garratt smothered a close-range finish from the striker whose searing 25-yard drive then just missed the top corner of the net.
And Harkins threatened to add to his goal when Garratt saved an angled drive with his legs in the closing minutes.
Chuks Aneke's late free-kick was tipped over by Oldham keeper Paul Rachbuka and from the resulting corner Davis headed Crewe's leveller in at the far post deep into stoppage-time.