Just a week after winning their first silverware for six years, United were put to the sword by Jurgen Klopp’s revitalised side on Sunday, collapsing as Liverpool smashed in six goals in the second half at Anfield.
Ten Hag’s men had travelled to the home of their biggest rivals with a spring in their step after just one defeat in 22 games and still on a high after beating Newcastle to win the League Cup at Wembley.
Their impressive run also included a landmark win against Barcelona in the Europa League as they chased success on four fronts.
But they came away from Anfield with their tails between their legs after the joint-heaviest defeat in the storied history of the 20-time English champions.
The humiliation ends fanciful talk of a potential quadruple, leaving third-placed United 14 points behind leaders Arsenal and well adrift of second-placed Manchester City.
Ten Hag was scathing in his assessment of his team, accusing the players of an “unprofessional” and “unacceptable” performance.
The wretched display shows how much work the Dutchman still has to do to rebuild a club that have not won the Premier League since 2013, despite unmistakeable signs of progress this season.
United had already endured an embarrassing 6-3 defeat at Manchester City this season, as well as a 4-0 loss at Brentford.
The debacle at Anfield was a new low but Ten Hag urged his team to use it as motivation for the rest of the season, starting in Thursday’s Europa League last-16 first leg at home to Real Betis.
“We have seen in the past we can bounce back — after Brentford, after Manchester City,” he told the BBC.
“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.”
– Horror show –
After an evenly matched first half, United were torn to shreds by a Liverpool team who themselves suffered the humiliation of a 5-2 Champions League defeat by Real Madrid last month.
The much-vaunted Casemiro was a bystander as the visitors were overrun in midfield and United’s defending was shambolic as the home team seemingly scored at will.
United skipper Bruno Fernandes came in for particularly harsh criticism from former United captains Roy Keane and Gary Neville.
Speaking after the final whistle, Keane told Sky Sports: “Fernandes’ body language today was nothing short of a disgrace, for me.
“He’s a really talented boy, he’s your captain. He’s got so much talent, but his body language, waving his arms and not running back…. You wouldn’t be happy with him in our dressing room, I’ll tell you.”
Neville said United’s showing was a “disgrace” but backed Ten Hag to turn things around quickly ahead of the Europa League clash with Real Betis.
“I think Erik Ten Hag will deal with them very, very strongly in this next 24, 48 hours — he’s done that already this season a few times — and I’d hope that basically normal service will be resumed by the end of next week,” he said.
United’s upcoming matches offer them a chance to get back on track, with relegation-threatened Southampton visiting Old Trafford after the Betis game.
Andy Mitten, editor of the United We Stand fanzine, urged calm and a sense of perspective despite the shock of the result at Anfield.
“I know there is a lot of emotion at the minute but United are still looking very comfortable in third, they are seven points clear of Liverpool,” he told the BBC.
“Not a chance I would have seen that at the start of the season. Won the League Cup, still in the FA Cup, still in the Europa League.”