The Latics were given a rough ride by Roses rivals Huddersfield, but Liddell's clever free-kick cancelled out Ian Craney's goal for the visitors.
Oldham went into the game with a 100 per cent home record and stood two points clear at the top of the table.
That gap has now disappeared as Huddersfield gave a combative display which provided more evidence that they are turning around their poor early season form.
The Terriers, who beat Northampton last weekend, almost scored in the first minute after good work by Liam Dickinson.
The on-loan Derby County striker was a real handful throughout the match and he set up Craney, who was denied by advancing goalkeeper Mark Crossley.
Oldham got on top for a spell as Lee Hughes and Chris Taylor - with 11 goals between them already this season - both went close from long range.
But Huddersfield made the breakthrough after half an hour when Dickinson's shot was deflected to Craney and the midfield man swept in from six yards.
Craney was only denied a quick second by Crossley and the save gained even more value on 49 minutes as Oldham pulled themselves level.
Liddell took charge of a free kick 25 yards from goal and hit a fizzing low shot into the bottom corner to leave keeper Matt Glennon wrong footed.
Both sides pushed for a second and Oldham's stand-in-captain Mark Allott, who was deputising for the suspended Sean Gregan, was thwarted by a brave block before Liddell suffered the same fate.
Huddersfield thought they should have had a penalty when Dickinson went down under a Reuben Hazell tackle, but Oldham went close near the end as substitute Chris O'Grady fired a shot just past the far post.