The hosts went ahead when Smith headed in Youssouf M’Changama’s cross.
Liverpool skipper Luis Suarez was allowed to run at the Oldham defence as he squeezed in an equaliser.
But Smith took advantage of keeper Brad Jones’s error and Reece Wabara scored a delightful back-post header as Oldham restored their advantage although Joe Allen’s volley ensured a tense finish.
Steven Gerrard, who was brought on from the substitutes bench with 35 minutes remaining in attempt to turn the game around, hit the bar as nerves frayed at a wet and windy Boundary Park.
Yet Paul Dickov’s side held on for a superb win over the seven-times winners on a weekend when Football League sides have caused upsets on all three days of the fourth round.
– bbc