Liverpool's 25-match unbeaten run came to an end on Sunday after falling to a 3-2 defeat to West Ham in a thrilling match at the London Stadium.
Jurgen Klopp's side would have broken the club's record unbeaten run in all competitions, which had stood since 1982, if they avoided defeat in London. But instead Alisson's disastrous display condemned Liverpool to a first loss since Real Madrid beat them in the Champions League quarter-final first leg in April.
It was a day to forget for Alisson, whose own goal put West Ham head in the first half.
Trent Alexander-Arnold equalised with a brilliant free-kick, but Alisson was at fault again as Pablo Fornals and Kurt Zouma struck for the Hammers after half-time.
Divock Origi got one back for Liverpool, but it wasn't enough to preserve their long unbeaten streak.
Liverpool dropped to fourth place in the Premier League as West Ham climbed above them into third place. The Reds are four points behind leaders Chelsea, while West Ham are only three adrift of Thomas Tuchel's men.
West Ham's first league win against Liverpool since 2016 was also their manager David Moyes' maiden league success against Klopp at the eighth attempt.
Moyes has worked wonders in his second spell at West Ham and a challenge for a Champions League place will be in their sights if they can maintain this level of performance.
It took just four minutes for West Ham to take the lead with a controversial opener.
Fornals' inswinging corner raced towards Angelo Ogbonna, who got in front of Alisson with a jump that obstructed the Brazilian's view.
Ogbonna's arm made contact with Alisson as the keeper's flailing attempt to punch clear diverted the ball behind him and into his own net.
A lengthy VAR check following as Liverpool's players surrounded referee Craig Pawson to claim both a foul on Alisson and a handball by Ogbonna, but the goal was allowed to stand.
There was more VAR angst for Klopp moments later when Aaron Cresswell escaped a red card for an ugly foul on Jordan Henderson that caught Liverpool's captain on his knee.
Klopp's smile briefly returned in the 41st minute as Alexander-Arnold brought Liverpool level.
Alexander-Arnold's first goal since April was just reward for an influential display from the right-back, who regularly moved into central midfield to help dictate Liverpool's attacks.
Having scored from their first corner, West Ham's second nearly brought another goal soon after the interval when Craig Dawson headed against the bar from Fornals' corner.
Liverpool's commitment to throwing bodies forward in search of the win came back to bite them in the 67th minute.
After Mane lost possession, Jarrod Bown embarked on a mesmerising run past a host of Reds' challenges before slipping a pass to Fornals, whose low shot from the edge of the area slipped under Alisson's weak attempted save.
Alisson's nightmare wasn't finished yet and the keeper was caught out of position at the far post as the unmarked Zouma headed West Ham's third goal from Bowen's 74th minute corner.
Origi scuffed home after Salah's shot deflected into his path in the 83rd minute.
Mane headed inches wide of the far post as West Ham survived a tense finale.