When the teams entered their dressing rooms for the interval, the scoreline read 4-0 to the visiting side.
Liverpool took advantage of an abject defensive display by Ole Gunnar Solskjaer's team, with Mohamed Salah wreaking havoc once again.
The Egyptian netted a brilliant brace and assisted Naby Keita's opening goal. Diogo Jota was the other man to get on the scoresheet in the opening 45 minutes.
It was utter humiliation for United and their supporters and things could have been even worse.
Late in the first half, star man Cristiano Ronaldo was incredibly lucky to stay on the pitch after he appeared to kick out at Curtis Jones in frustration.
Liverpool players were fuming with the 36-year-old's reckless actions and it looked for all the world that VAR would review the incident and deem it worthy of a red card.
But Ronaldo somehow got away with just a yellow.
Take a look at the five-time Ballon d'Or winner's clash with Jones here...
Video: Ronaldo kicks out at Jones
Is that a red card offence? There's a strong case to be made that it is.
Ronaldo simply lost his head and then endangered an opponent, which is more than enough to warrant being dismissed from the field of play.
The former Real Madrid and Juventus player is certainly no stranger to a red card.
Ronaldo has been sent off 11 times in his career and he's mighty lucky that number 12 didn't come at Old Trafford on Sunday.