Striker Matt Smith chose the perfect occasion to score his first goals at Boundary Park as his first-half double helped League One Oldham produce an FA Cup upset in beating Liverpool.
The 23-year-old, who 18 months ago was playing non-league football with Solihull Moors, had the best day of his fragmented professional career after giving the Reds' defence a torrid time.
He scored either side of Luis Suarez's 21st of the season in the first half before Reece Wabara's header put the Latics into the last 16 despite Joe Allen's goal 11 minutes from time.
It was the first time Liverpool had been beaten away from home in the FA Cup by a team at least two divisions below them since defeat at non-league Worcester City in 1959.
Smith had given up on professional football after being released by Cheltenham aged 18 and went on to gain a degree in International Management with American Studies from the University of Manchester.
While studying he played for the likes of Redditch United, Droylsden and Solihull Moors - where he was spotted by Oldham.
Prior to this game he had scored only scored seven times in 60 appearances for the Latics but none will have been as enjoyable as his two in the first half against the seven-time FA Cup winners from the Barclays Premier League.
Liverpool manager Brendan Rodgers' decision to alter three of the back four among six changes proved calamitous as infrequent starter Sebastian Coates had a game to forget.
Oldham, with only one win in their last nine games, had beaten progressively higher-ranked opposition in Kidderminster, Doncaster and Nottingham Forest to reach the fourth round for the first time in five years.
But it was not fate which got them through as the Latics' no-nonsense, battling approach deservedly put them ahead.
Smith gave indication of his threat in just the third minute with the sort of goal you associate with a player of his physical stature.
Youssouf M'Changama swung over a cross from the left and the 23-year-old used every inch of his 6ft 6in frame to out-muscle Coates and head past Brad Jones.
The first half had an edge to it as Oldham, having taken one point from a possible 24 in the league, tried to close the gap of 56 places with endeavour and exuberance.
However, it was Liverpool youngster Raheem Sterling who was first to be booked for challenge on M'Changama which ultimately forced the Oldham midfielder off after just 10 minutes.
Robbie Simpson, a scorer at Anfield in Oldham's 5-1 third-round defeat last season, was also cautioned for going in on Jones after the goalkeeper had failed to hold the ball - which turned out to be a pre-cursor of what was to come.
Former Everton midfielder Jose Baxter did his best to make life difficult for the red half of Merseyside, twice shooting wide from distance, but it was Suarez who was next to feature and significantly so.
The Uruguay international, captaining the side, set off on a driving run from deep and looked to pass but got a lucky rebound off defender Cliff Byrne and reacted quickly to hammer the ball inside Dean Bouzanis' left-hand post.
It was his fifth goal in six FA Cup appearances and his eighth strike in as many games.
His touch to Jordan Henderson's inswinging free-kick then diverted the ball into the net only to be denied by an offside flag.
Sterling should have scored after Suarez's pass was backheeled into his path by Fabio Borini but he shot straight at the keeper.
But Oldham remained unbowed as they took great heart from the physical battles they were winning and were rewarded with a second goal moments before the interval.
Smith, who had already had a header tipped over by Jones in added time, converted the simplest of chances after a howler by the Liverpool goalkeeper who fumbled Wabara's cross to allow Simpson to square a pass for the striker to poke home.
Borini had the chance to equalise from Jack Robinson's cross with the second half less than a minute old but he side-footed over and it proved costly.
The visitors' defensive fallibility in the air was exposed again as Carl Winchester swung a cross to the far post and Wabara rose above Robinson to head over Jones into the far corner.
Steven Gerrard's introduction from the bench was not long in coming and the England captain soon had a shot blocked from which Daniel Sturridge blazed over.
Allen pulled one back with 11 minutes to go to with a shot which deflected in off Baxter but Oldham held on to reach the fifth round for the first time in 19 years.
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