Liverpool maintained their flawless start under new manager Arne Slot as they outclassed woeful Manchester United at Old Trafford.

The visitors were on a different level to United in a win so comprehensive that it will bring renewed scrutiny on Slot's fellow Dutchman Erik ten Hag, who survived a summer review to win a new contract following last season's FA Cup win.

Liverpool have barely missed a beat since Slot replaced Jurgen Klopp, recording three straight Premier League wins now without conceding a goal, and this was the most impressive display so far.

Trent Alexander-Arnold had already had a goal disallowed for offside before Luis Diaz struck twice in quick succession just before the interval to put Liverpool in complete command.

Casemiro, who endured a first-half nightmare before being replaced, was the culprit twice as he conceded possession, with Diaz heading home Mohamed Salah's cross at the far post after 35 minutes before sweeping in the Egyptian's pass in front of the Stretford End seven minutes later.

Salah, inevitably, got in on the act with his 12th goal in 15 appearances against United after 56 minutes, beating Andre Onana from Dominik Szoboszlai’s pass.

United had opportunities, mainly through Joshua Zirkzee, but there were only occasional moments of anxiety for Liverpool as they put Ten Hag's side firmly in their place.

United manager Ten Hag wanted a fast start after keeping his job in the summer, an outcome that was surely helped by the FA Cup final win over Manchester City.

The lack of a credible and available alternative also appeared to play into the decision-making process of co-owner Sir Jim Ratcliffe and the new Old Trafford hierarchy.

Rather than roar out of the blocks, though, United have snatched a win with a late goal against Fulham at Old Trafford before losing at Brighton, and now they have been swept aside by Liverpool.

There were jeers from United's fans at half-time and the end here, as well as when Ten Hag replaced Alejandro Garnacho with Amad Diallo in the second half.

He had already been forced to make what was effectively a mercy change at half-time, replacing Casemiro after a grim display in which he helped Liverpool score their first two goals by conceding possession too easily.

It made for an uncomfortable afternoon for Ratcliffe, watching grim-faced from the directors' box as the hope of a new start was punctured by the pain of watching Liverpool tear United apart.

There were mitigating circumstances for Ten Hag, with the new signing from Paris St-Germain, Manuel Ugarte, not available to play. Another summer acquisition in Leny Yoro is injured, as are Mason Mount, Luke Shaw and Rasmus Hojlund.

Such factors cannot disguise, however, the lack of quality in this United side as Liverpool taught them a harsh lesson in control, intensity and end product.

This was exemplified by the sight of Casemiro, the once great midfield man at Real Madrid, who looked a spent force last season and would have left in the summer had United been able to find a buyer, playing so poorly that Ten Hag was prepared to send on 20-year-old Toby Collyer to replace him for the second half.

The Premier League season may only be in its infancy but defeats of this nature will inevitably put Ten Hag under the microscope in such a vital campaign – and the problem with handing a manager what effectively appeared to be a stay of execution is that they are always one bad result away from speculation.

This is why this meeting with old adversaries Liverpool was so vital and the manner in which United were beaten may prove to be so significant.

Premier League newcomer Slot made a smooth start at Liverpool with victories away at newly promoted Ipswich Town and at home against Brentford – but a trip to Old Trafford was regarded as the first serious examination of the new post-Klopp era.

This emphatic win came at a ground where Klopp’s Liverpool lost in the FA Cup quarter-final last season and were also held to a draw in April, a result that damaged their chances of challenging Arsenal and Manchester City in the title race.

Those two games were perfect examples of the wonderfully entertaining, but occasionally chaotic, brand of football Klopp delivered at Liverpool as they lost control on both occasions after dominating.

Slot still has all of Liverpool's attacking tools at his disposal but is clearly intent on adding a layer of measured control to their style, which his team showed here as they were never in danger of relinquishing their hold on affairs once Diaz had given them that two-goal advantage.

On the rare occasions United did threaten, Liverpool goalkeeper Alisson demonstrated his world-class quality, frustrating the erratic Zirkzee in particular.

In pretty much every other respect, this was business as usual for Liverpool - a side full of threat, especially in the shape of Salah, who has made such a habit of tormenting United and did so again.

This was, however, a complete Liverpool performance which left Slot and his players taking the acclaim of their elated supporters at the final whistle.

And as Slot's name rang out, the Dutchman responded with a modest wave and a clenched fist. There were none of Klopp's trademark fist pumps, but the deafening roars from the travelling fans suggested the new boss has already won those Liverpool hearts.