In hindsight, this outcome was entirely predictable.
The Premier League's most lethal attack - Liverpool had scored 30 goals in their previous nine games in all competitions - against a defence that had shipped six goals in the last week and kept one clean sheet in the last six months.
"It's what I said," said Gary Neville after Mohamed Salah had rattled home Liverpool's fourth, "the minute they play a proper team, this is what's going to happen. If half-decent teams are scoring so many goals against them, proper teams will batter them."
Still, though, the extent of the collapse felt extraordinary. This Manchester United side have shown a knack for conjuring up results when they need them most but not this time. Not when they allow their opponent a four-on-one attack inside five minutes.
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That opening goal, when Liverpool sliced through United like a knife through butter and Naby Keita slid home from Salah's pass, set the tone for the chaos that followed.
They were fortunate not to be two goals behind barely two minutes later, when Scott McTominay and Fred combined to lose possession in their own defensive third - teamwork, at least, albeit not the kind United had in mind - and Roberto Firmino fired straight at De Gea.
But Liverpool did not have to wait long.
The second goal came just eight minutes after the first and it was another exhibition in shambolic defending. Harry Maguire and Luke Shaw lost their heads, and Trent Alexander-Arnold, while Aaron Wan-Bissaka failed to track the onrushing Diogo Jota.
It got worse. Much worse.
United survived the next 25 minutes without conceding but only just.
In that time, Firmino wastefully fired wide from a Keita cross-shot, while there was even the bizarre sight of Marcus Rashford's attempted backpass, played from 10 yards inside Liverpool's half, sending Salah through on goal.
De Gea denied the Egyptian on that occasion but it summed up the surrealness of the occasion nonetheless. Soon enough, the carnage continued. Keita, like Alexander-Arnold before him, had all the space he could possibly wish for to tee up Salah for the third.
Manchester United did not learn. In fact, Liverpool's next goal, arriving just before half-time and ensuring United trailed by four at the interval for the first time in Premier League history, came from the exact same place, Salah simply picking his spot.
Any hope that the half-time whistle - greeted with loud boos by the home supporters - might allow Manchester United to regroup evaporated within a few minutes of the game's resumption.
This time, it was substitute Paul Pogba who lost possession. One Jordan Henderson pass later, Salah was celebrating his hat-trick.
"This is as bad as it gets," said Neville. "We've all lost football matches in a bad way. Sir Alex Ferguson once lost a game 6-1 against Manchester City. I lost a game away at Newcastle 5-0. But it's the nature of the performance. They have capitulated."
Pogba's straight red card added to the ignominy of the occasion and it was damning, too, that Liverpool were able to inflict such a brutal defeat on them with an understrength team.
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Their midfield of Henderson, Keita and James Milner was rightly described as "workmanlike" by Jamie Carragher - the visitors even lost the latter to injury just 27 minutes in - and yet they outplayed their counterparts in every respect.
Klopp left Sadio Mane on the bench but Liverpool had scored five goals by the time he was introduced. He started with Ibrahima Konate at centre-back, the Frenchman making only his second Premier League start, but United barely even tested him.
"What we've seen is a team versus individuals," said Carragher.
The structure and organisation Klopp has put in place ensures Liverpool can lose personnel without losing their identity. But where is the structure and organisation in this Manchester United side? What even is their identity under Solskjaer?
It is almost three years since his appointment at Old Trafford but there is still no clear answer to that question. A summer of heavy investment was supposed to take United to the next level but it appears to have muddied the waters further.
Cristiano Ronaldo has papered over the cracks at times but Manchester United look less like a serious team with every passing game. They have lost any semblance of cohesion in the final third but it is at the other end that the issues are most apparent - as they have been all season.
Only Watford, Newcastle, Leeds and Norwich have conceded more goals in the Premier League so far. No side has made more errors leading to shots than Manchester United.
They were supposed to challenge for the title this season but they have allowed their opponents more efforts on target in the last two games than Manchester City have all season. They conceded more goals in 45 minutes at Old Trafford on Sunday than City have in 810 minutes since the start of the campaign.
The numbers make grim reading for Solskjaer, the man tasked with moulding Manchester United's individuals into a team, and the worst thing of all is that, really, this historic defeat was entirely predictable. "It had been coming," added Neville. There is a growing feeling of inevitability about what comes next for Solskjaer too.
Man Utd's defensive disasterclass in pictures
It doesn't get much easier for Manchester United; they face a formidable set of fixtures over the next six weeks as they look to keep pace in the Premier League and ensure Champions League qualification, with Chelsea, Arsenal, Tottenham and the Manchester derby looming domestically.
October 30: Tottenham (a) - Premier League, kick-off 5.30pm, live on Sky Sports
November 2: Atalanta (a) - Champions League, kick-off 8pm
November 6: Man City (h) - Premier League, kick-off 12.30pm, live on Sky Sports
November 20: Watford (a) - Premier League, kick-off 3pm
November 23: Villarreal (a) - Champions League, kick-off 5.45pm
November 28: Chelsea (a) - Premier League, kick-off 4.30pm, live on Sky Sports
December 2: Arsenal (h) - Premier League, kick-off 8.15pm