As Trent Alexander-Arnold left the field, he gazed up at the joyous scenes in the Main Stand and raised seven fingers in celebration.
The Liverpool right-back is well-versed in what this fierce rivalry means and the look on his face perfectly encapsulated the mood inside Anfield — part euphoria, part astonishment.
All the talk pre-match had been about a shift in the balance of power between English football's two most successful clubs. Manchester United's transformation under Erik ten Hag this season had been accompanied by Liverpool's regression.
United, without a victory at Anfield for seven years and buoyed by their Carabao Cup triumph, smelt blood. Yet they were given the most brutal of reality checks on a day that will be remembered forever.
The word defeat doesn't begin to do justice to what transpired. This was complete and utter humiliation. Forget the prize for Jurgen Klopp's side was only three points, it will have much bigger ramifications. We've never seen the like before and are unlikely to ever do so again. Drink it all in.
It was the biggest margin of victory in 211 meetings between the clubs, eclipsing Liverpool's 7-1 win in 1895 (when United were known as Newton Heath). It also equalled United's heaviest-ever defeat, sitting alongside their other 7-0 hidings at the hands of Wolves (1931), Aston Villa (1930) and Blackburn Rovers (1926).
“We want eight,” crowed the Kop during the closing stages as their embarrassed visitors longed to be put out of their misery.
For Liverpool, this was dreamland. The sight of United pummelled into submission — the away end emptying long before the end.
Suddenly, a season that appeared beyond repair now boasts the most remarkable of energising chapters. Suddenly, talk of pulling off a miraculous Champions League salvage act in the Bernabeu next week doesn't appear so preposterous.
Not when Liverpool attack with this kind of blistering pace, incision, fluency and ruthless streak. Not when they defend so well as a unit. Not when key personnel have rediscovered their mojo. Not when belief has been restored so emphatically.
Imagine being told a month ago, in the aftermath of that wretched, lifeless 3-0 defeat to Wolves at Molineux that Liverpool would be in this position – three points behind fourth-placed Tottenham with a game in hand.
Back then, Klopp's men were a mess and the manager cut an agitated figure as he wrestled with the biggest crisis of his reign. His team were blunt at one end and horribly vulnerable at the other. It was all so disjointed. They had taken just one point out of 12. They had conceded three goals in three successive away league games for the first time since 1993.
Taking in Manchester United's worst defeat since 1931 (Photo: Michael Regan/Getty Images)
What's changed? How have they taken 13 points out of the last 15 on offer and kept five successive league clean sheets?
The return to fitness of centre-backs Virgil van Dijk and Ibrahima Konate has massively helped. They complement each other so well and have provided the kind of leadership and composure that was previously missing.
Just as crucial has been the resurgence of Fabinho after a torrid spell. Only one Brazilian holding midfielder shone at Anfield and it certainly wasn't Casemiro. Fabinho, who made three interceptions, was helped on Sunday by the experience of captain Jordan Henderson on one side and the youthful exuberance of Harvey Elliott on the other, who each claimed an assist.
No one on either side gained possession more times than Henderson (11), while no one ran further (10.1 km) or completed more passes than Elliott (45). Liverpool's balanced midfield trio all made telling creative contributions in the final third as the hosts repeatedly countered with menace.
Going forward, Liverpool sparkled as their front three ran riot. What was most refreshing was the sight of them going for the jugular in the second half after Cody Gakpo had slammed home the opener following an exquisite pass from the outstanding Andy Robertson.
There have been flashes of brilliance previously, but here was the first real sustained onslaught from Klopp's new-look frontline. Yes, United pitifully capitulated, but Liverpool were gloriously relentless.
They out-flanked United to sign Gakpo from PSV Eindhoven in the January window and, after a difficult start, the Dutch striker is really blossoming, just like Darwin Nunez before him. Patience is a virtue. You can see the value of time spent on the training field. Now they are looking the part.
Gakpo and Nunez, both aged 23, are the future and the understanding between them is growing. To score two apiece in a game of such magnitude will only help push them on to the next level.
What a day for the old guard, too. Mohamed Salah became the club's highest Premier League goalscorer, overtaking Robbie Fowler's tally of 128 despite playing 61 fewer games.
“It's very special, I can't lie,” Salah said. “This record was in my mind since I came here. I think after my first season I was always chasing that record. To beat it against United with that result is unbelievable. I'm going home to celebrate with the family, have a camomile tea and sleep.”
The Egyptian, who scored two and created another two, has now netted 12 goals in 12 appearances against United – more than any other Liverpool player. How he tormented Lisandro Martinez.
The noise when Salah flung his shirt away and accepted the acclaim of Anfield after scoring the sixth was incredible. However, the outpouring of emotion that followed Liverpool's seventh was cranked up another level.
Liverpool's goalscoring king is crowned (Photo: Andrew Powell/Liverpool FC via Getty Images)
How fitting that substitute Roberto Firmino should have the final word, nutmegging David de Gea after confirming he will end his eight-year stay at the club when his contract expires this summer. His team-mates raced to share the moment with him.
“Freak result, top performance. A really special night,” Klopp said. “I think everybody saw how good the boys can be.”
Of course, it doesn't change the need to strengthen this summer. But it should silence some of the nonsense about a complete overhaul being required. There's still a serious amount of talent in this squad and United felt the full force of it.
Yes, Liverpool have underachieved this season. Yes, they must make this result count by kicking on and salvaging a top-four finish. But let's not play down the significance of it.
It was a day when the frustration of this season was washed away in sparkling fashion. Liverpool 7 Manchester United 0. This was seismic. This was history.