Darren Sheridan opened the scoring with a fierce 25-yard shot in the 24th minute and Liddell increased the lead 13 minutes later, latching onto an astute pass by Neil Thompson to beat Reading goalkeeper Sal Bibbo from close range.
Reading were reduced to 10 men when Andy Bernal brought down Liddell in the 80th minute and, to compound the Royals' misery, Liddell swept in Thompson's inswinging corner two minutes later.
At the Victoria Ground, an injury-time penalty by Mike Sheron maintained Stoke's 100 per cent record and condemned Bradford City to a 1-0 defeat.
The visitors were playing out time, having had few scares, but Richard Liburd's foul on Ally Pickering allowed Sheron to strike his fourth goal in three games for Stoke this term. Barnsley, who have scored more goals, and Stoke are the only First Division sides with maximum points from three games.
Steve McMahon's Swindon secured their first win since returning to the First Division thanks to a second-half Wayne Allison goal against Oldham.
There was little for the crowd to get excited about until the 59th minute, when Allison rose above the Oldham defence to meet a deep cross from Mark Seagraves and nod a header downwards past Jon Hallworth. .Reuse content