The Reds slipped to a first defeat to a team from the third tier in 20 years, as giant Latics forward Matt Smith nodded his side on the way to a 3-2 win in the opening seconds.
Captain Luis Suarez equalised for the Reds, but just when Liverpool looked like they were taking control of the contest and easing to the win that many expected them to achieve, Smith profited from an error from goalkeeper Brad Jones to restore Oldham’s lead on the stroke of halftime.
Reece Wabara’s fantastic header made it 3-1 early in the second half, and although Steven Gerrard appeared from the bench to try to inspire Liverpool to yet another cup comeback, one never materialised.
A deflected volley from Joe Allen raised the Reds' hopes, but Gerrard’s thunderous strike from distance against the crossbar in the closing moments summed up Liverpool’s day as they slipped to a demoralising defeat.
Here are some lessons learned from Brendan Rodgers’ most depressing day in the Liverpool hot seat.