ARNE SLOT earned Liverpool an imperious win on his first visit to Old Trafford - with one tactic making a key impact.
Manchester United errors gifted Liverpool three goals but the Red Devils were second best all over the park.
Liverpool took a two-goal half-time lead as Luiz Diaz scored twice from inside the penalty area.
Casemiro misplaced a pass for the first goal and was then dispossessed for the second.
The Brazilian has been a constant weak point for Man Utd in the past 12 months, but he was far from the only underperforming star for the Red Devils as they went down to a 3-0 loss.
Kobbie Mainoo was caught on the ball for the third Liverpool goal while Lisandro Martinez also failed to impress.
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But stats show that Liverpool's win may have been, more than anything, down to Slot keeping one of United's biggest stars quiet - Alejandro Garnacho.
The young winger has been one of United's best players in the last year and even when the team is not playing well he has produced moments of magic.
But against Slot's Liverpool, nothing came off for Garnacho - he was dispossessed on several occasions and completed just 16 passes.
Liverpool's tactics meant Garnacho rarely received the ball in the attacking final third and he constantly had to drop deep to receive possession.
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That meant his average position was at right-back rather than on the wing, with the Argentine making just three touches in the Liverpool box.
Remarkably, of his 16 completed passes just four were forward, with one coming in his own penalty area.
As a result, he had very little impact on the United attack with most of his afternoon's work coming in a defensive capacity.
Slot gave the dangerous Luis Diaz the freedom to push forward, meaning Garnacho was often called on to support his full-back Noussair Mazraoui.
And the Argentine's ineffectiveness would ultimately lead to boss Ten Hag hooking him off for Amad Diallo.
But the decision was far from a popular one with a number of fans at Old Trafford booing the substitution.
Some fans even went as far as to say Ten Hag was "sacking himself" with such a "nonsense" call.
Man Utd player ratings vs Liverpool

MANCHESTER UNITED had a horror show against Liverpool as they lost 3-0.
Casemiro was so bad he was taken off at half-time.
But were there any positive performances at Old Trafford?
Andre Onana - 5
Nothing he could do about any of Liverpool's goals and made a few saves to prevent the scoreline from getting worse.
Noussair Mazraoui - 5
Came close to scoring in the first half and looked solid enough against Diaz although he did push up too high before Liverpool's opener.
Matthijs de Ligt - 4
Left Diaz and Domink Szobozslai in acres of space for the opening goal but was left in a tricky spot thanks to Casemiro's error.
Booked for a shocking late tackle on Diaz.
Lisandro Martinez - 3
Lost Diaz for the second goal which meant the Colombian was able to score unmarked from the penalty spot.
Also guilty of giving away the ball too easily and was not tight enough with his marking.
Diogo Dalot - 4
Was caught out pushing up too quickly for the first goal and did not do enough to stop Mo Salah's cross in the build-up to Liverpool's second.
Looked dangerous in attack at times but too infrequently as he had plenty of defensive work to do since Rashford did not track Trent Alexander-Arnold.
Casemiro - 2
A horror show in the first half as he gave the ball away in the lead up to both of Liverpool's goals.
He was caught on the ball for the second after a shocking misplaced pass left his defence vulnerable for the opening goal. Hooked at half-time.
Kobbie Mainoo - 4
Fell victim to the Casemiro curse as he was shrugged off the ball in a terrible position, allowing Liverpool to add a third with ease.
Bruno Fernandes - 5
Was United's most creative spark but that is not saying much. Tried to get his side going in the first half but looked short of ideas and inspiration after the break.
Alejandro Garnacho - 4
Still appears to be a little rusty and is yet to hit the heights he reached last season.
Marcus Rashford - 3
Nothing came off for the out-of-sorts forward who must be running out of chances before he is dropped.
Joshua Zirkzee - 4
Quiet up-front and had little influence on the wing as well, but missed a clear-cut chance with his head and should have turned in Rashford's cross which he met at the far post.
Subs
Tom Collyer (for Casemiro, HT) - 5
A difficult game for the youngster to make his Premier League debut but he put himself about and won a few tackles.
Harry Maguire (for De Ligt, 69mins) - 5
Shored things up at the back as Liverpool took their foot off the pedal.
Amad (for Garnacho, 69mins) - 5
Provided a spark on the right and looked more lively than Garnacho.
Christian Eriksen (for Zirkzee, 86mins) - N/A
Not on long enough to make an impact.
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