Leicester were on course to seal their fifth win in six away games after Steve Howard fired them ahead, but Oldham hit back with a superb goal by midfield man Danny Whitaker.
Both teams were protecting proud, unbeaten records - Oldham at home, Leicester on their travels - and there was little to choose as they each enjoyed spells in charge.
Howard was denied by the woodwork before claiming his fourth goal of the season while visiting keeper David Martin had to make two good saves.
Leicester were without defender Aleksander Tunchev as he arrived back from international duty too late, but it was Oldham who showed more changes despite hammering Hereford 4-0 last week.
Boss John Sheridan shook up his team, only to be forced into another re-shuffle when defender Richie Byrne was forced off in the first 15 minutes.
There were few chances early on but Leicester went desperately close in the 30th minute when Matt Oakley prodded goalwards and Whitaker appeared on the line to make a vital clearance.
Howard hit the post with a towering header ten minutes later and winger Lloyd Dyer was left holding his head after latching on to the rebound and blazing it over the bar.
Lee Hughes headed wide from a corner at the other end but Leicester struck on 54 minutes after winning a controversial free-kick on the right.
Dyer crossed towards the far post and Howard jumped the highest to send his powerful header past the stranded Mark Crossley.
Oldham's reaction was impressive and Mark Allott tested Martin before the equaliser stemmed from a right-wing cross.
Chris Taylor touched the ball to Whitaker, whose 22-yard shot floated into the top corner with perfect accuracy.
Both sides pushed for the winner but Oldham's Daniel Jones missed by inches from the edge of the box and left the winger Max-Alain Gradel wasted a chance on the counter-attack.