Robbie Simpson’s ninth goal of the season looked set to give the Latics maximum points in a dour contest, but Chris Holroyd pegged them back 11 minutes from time.
Oldham wasted a good early chance when Simpson blazed wide from Youssouf M’Changama’s pass. Oumare Tounkara also missed the target from close range before Preston went close twice within a minute, Holroyd forcing a save from Dean Bouzanis and Craig Morgan heading over from eight yards.
Oldham captain Dean Furman saw his goalbound shot blocked, but Simpson again failed to test visiting goalkeeper Thorsten Stuckmann when well placed in the box.
However, Simpson broke through after 69 minutes, glancing in a six-yard header from a left-wing free-kick by Filipe Morais.
Preston levelled 10 minutes later as Danny Mayor chipped in a neat cross from the left and Holroyd had the simple task of nodding home from two yards out.