Erik ten Hag said his Manchester United players were "unprofessional" in an "unacceptable" performance at Anfield as Liverpool inflicted a 7-0 defeat that equals the club's heaviest-ever loss.
Two goals each from Darwin Nunez, Cody Gakpo and Mohamed Salah, who became Liverpool's all-time top Premier League scorer, and one from Roberto Firmino gave Liverpool their biggest win against United and equaled the visitors' all-time worst defeat of 7-0 against Blackburn Rovers in 1926, Aston Villa in 1930 and Wolves in 1931.
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United have now failed to win at Liverpool since January 2016, and have scored just once in their past seven trips to Anfield, but their performance on this occasion saw them concede six goals in the second half Sunday.
And after seeing his team capitulate, United manager Ten Hag said the defeat delivered a reality check for the club just a week after it ended a six-year trophy drought by winning the Carabao Cup.
"Second half, it was just not us," Ten Hag said. "It was not our standards. We didn't play as a team. It was unprofessional. Yes [I am angry]. Definitely.
"I am surprised because I have seen the last weeks and months this team is resilient and has a winning attitude.
"Second half, we didn't have a winning attitude at all. We didn't stick to the plan and we didn't do our jobs. We didn't track back and it was really unprofessional.
"We have seen in the past we can bounce back. After Brentford, after Manchester City. This is definitely a strong setback and is unacceptable. I'm really disappointed and angry about it. It is a reality check. We have to take this strong."
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Former United captain Roy Keane was equally critical of his former team, labelling them "embarrassing."
"A shocking day," Keane told Sky Sports. "The senior players were embarrassing. They didn't show any leadership skills. A really tough day for Man United and thank goodness I have never been part of losing like that.
"The players will be ashamed when the going got tough, they went missing. I never thought United were back to their very best. They have been giving teams chances but today Liverpool didn't let them off the hook."
Liverpool manager Jurgen Klopp said the win, which took his team to within three points of Spurs in the top four, was "perfect."
"No words. It was a spectacular football game. Outstanding," Klopp said. "We played top football against the team in form. It was a bit wild in the first half, but the second half the start was pretty good and the end was pretty good. Everything was pretty good. That is football, it can happen, and we got three very important points.
"It was the push we wanted. It puts us in the right direction. Everyone has to know we are still around. It wasn't the case for a while, but tonight was a proper show of what we can be and what we have to be from now on. There are 13 games to come, a lot of points to come, but today was perfect."