The spectre of racism and the Luis Suarez T-shirts once more overshadowed Liverpool as a fan sporting the top worn to support the banned striker confronted Oldham's young defender Tom Adeyemi and reduced him to tears.
The supporter approached Adeyemi during the game and the player is believed to have given a statement to police that he was called "a black c***".
The Oldham manager, Paul Dickov, said: "I don't know the details but something has been said. Tom is a 20- year-old boy who has been well educated and has a fantastic temperament. We have had him since the end of August and I have never seen him raise his voice, so for him to react like that, something has been said."
Liverpool issued a statement acknowledging that an incident occurred in the second half and said it was being investigated by both the club and the police, although no arrests were made.
The actions of one supporter in a capacity crowd that contained Suarez succeeded in marring not just the first anniversary of Kenny Dalglish's return to Anfield but of a fine performance from Oldham that the Liverpool manager conceded could not be measured by the scoreline.
The night began very differently from the way it ended with a passionate minute's applause for Gary Ablett, whose death at the age of 46 is a reminder that life is infinitely crueller than football. It will be a long time before anyone repeats his feat of winning the FA Cup with both Liverpool and Everton.
Since Steven Gerrard lifted the FA Cup in 2006, no Liverpool player has come remotely close to the final. This marked only their second victory over a current League club since that helter-skelter day in Cardiff – previously they had beaten only Preston who lie a single place above Oldham in League One.
Dickov pointed out that his team, under-funded and reliant on loan players like Adeyemi, who they borrowed from Norwich, and Robbie Simpson, who struck the night's first and most memorable goal, perform better against better teams. The opening half an hour seemed to support that theory.
Whatever happened to them subsequently, the goal would live long in Oldham's collective memory. Simpson took a short pass, looked up and delivered a left-foot shot from more than 20 yards that finished in the corner of Pepe Reina's net beneath the Kop. Simpson ran most of the length of the pitch and slid into the arms of his keeper, Alex Cisak. You could understand why.
Nevertheless, watching from the sidelines, Dickov would have wanted rather more calm, but the smoke from the fireworks among the 6,100 who had travelled across Lancashire had barely cleared when Liverpool were level.
Jonjo Shelvey, cutting in from the right, let loose a shot that Craig Bellamy flung himself at and deflected past a stranded and already-committed keeper. It was either brilliant judgement or a slice of considerable fortune.
Oldham were starting to slide and just before the interval they fell. Maxi Rodriguez was pushed in the box by Adeyemi and Gerrard stepped up to take the penalty and shatter some dreams. Dickov called the award "a joke".
Thereafter, Liverpool's control was total. Bellamy was rampant down the right flank and but for a wonderful save from Cisak his pace and low crosses would have produced more than one goal. Nevertheless, when he opened up Oldham's defence for Liverpool's third scored by Shelvey, Dickov, along with everyone else, knew the game was up.
It still had to be played out, however, and Dalglish pressed home his advantage by introducing two footballers who could do with a performance and a goal. Stewart Downing scored the fifth, while Andy Carroll, brought on for the last rites, struck spectacularly from the edge of the area. In the space of a week Merseyside has witnessed goals from Tim Howard and now Carroll. Strange Days to quote the John Lennon song they played on the final whistle.
Liverpool (4-2-3-1): Reina; Kelly, Coates, Carragher, Fabio Aurelio (Flanagan, 71); Gerrard, Spearing; Shelvey, Bellamy (Downing, 74), Rodriguez; Kuyt (Carroll, 87). Substitutes not used: Doni (g), Henderson, Adam, Skrtel.
Oldham Athletic (4-4-1-1): Cisak; Adeyemi, Mvoto, Diamond, Lee; Scapuzzi (Parker, 54), Wesolowski (Morais, 74), Furman, Taylor; Simpson (Smith, 74); Kuqi. Substitutes not used: Bouzanis (g), Tarkowski, Black, Mancini.
Referee: N Swarbrick (Lancashire).