A Mohammed Salah hat-trick and a disorganised Manchester United defence helped Liverpool thrash the 20-time English champions 5-0 in their own backyard.
Naby Keita and Diogo Jota were the other scorers as United's Paul Pogba received a straight red card in the 60th minute.
The floodgates opened for Liverpool early on in the game when Salah's through ball in the fifth minute found Naby Keita who scored past United goalkeeper David de Gea.
Just eight minutes, Liverpool would double their lead when a defensive mix-up between United's Harry Maguire and Luke Shaw allowed Trent Alexander-Arnold to drill in a low cross that found an unmarked Jota creep in a score from the far post.
From there on, it was the Mo Salah show.
Salah slammed the ball in for his first from a Keita cross and then got his second and the team's fourth from a low effort late into the stoppage time of the first half.
As the teams walked off the pitch for the break, the boos rained down on the home team, with fans even leaving the stadium for good.
The talismanic French midfielder Paul Pogba was brought on for the underperforming Mason Greenwood, but a lunging tackle the substitute would make on Keita in the 60th minute would earn him a red card, reducing United to ten men.
But by then, the destruction had been complete, as Salah completed his treble ten minutes before Pogba's sending off.
The Egyptian, who is in the form of his life, became the first visiting player to score a league hat-trick at Old Trafford since 1991 when he latched on to a Jordan Henderson pass to finish off the game in style.
Liverpool cruised home after that, keeping possession of the ball as the stadium emptied out.
The defeat piles on additional pressure on United coach Ole Gunnar Solskjaer, who has been repeatedly criticised for his inflexible tactics and the inability to get the best out of a star-studded squad.
“It is not easy to say something apart from that it is the darkest day I have had leading these players,” said Solskjaer after the game.
United's last five-goal defeat at Old Trafford was the 6-1 humbling by neighbours Manchester City in 2011.
