Manchester United ran riot in the first half as they beat Premier League champions Leicester 4-1 at Old Trafford.

Chris Smalling set the ball rolling before Juan Mata, Marcus Rashford and Paul Pogba all found the net before the break, as United wrapped up three easy points on an afternoon where Wayne Rooney was dropped to the bench.

Here, Sportsmail's Chris Wheeler looks through the lessons we learned as Mourinho's side got back to winning ways in the Premier League after two-straight defeats.

Paul Pogba looked to the heavens after scoring his first Manchester United goal

Jose Mourinho's side ran riot in the first half before ultimately beating Leicester 4-1

Marcus Rashford slides in to convert United's third goal from close range

Jose Mourinho's old siege mentality is still having an effect after all these years

In the wake of three straight defeats, he used his programme notes to galvanise the club in the face of outside criticism – or ‘Einsteins’ as he referred to them beforehand.

‘During the week we are not on holiday, we have no time for posh dinners in restaurants, we don’t feed the vanity of the opinion-makers,’ he wrote. ‘The boys need support after hearing and reading cruel comments. They read them, their families read them and they feel them.’

Jose Mourinho showed his old siege mentality in the wake of criticism ahead of the game

Wayne Rooney has to accept he is a squad player now

He was a guaranteed starter under Louis van Gaal, and Mourinho kept him as captain in the No.10 role, but Rooney can no longer be a shoe-in for this team.

The moment he was taken out of the firing line, United scored four goals in the first half. Juan Mata offered more creativity in the No 10 role.

The England captain will come again. He’s not finished yet by some stretch. But he will have to accept less game time and a more peripheral role at times.

Wayne Rooney now has to accept his role as a squad player at Manchester United

Leicester need to get back to basics

Jamie Vardy and Riyad Mahrez may have lit up the Premier League last season, but first and foremost the club’s stunning title success was built on solid defence.

Despite Kasper Schmeichel’s injury problems and the departure of defensive kingpin Ngolo Kante, Claudio Ranieri has been able to call on the same back-four but at the moment they look vulnerable.

At Old Trafford they were guilty of switching off on several occasions, not least the three goals United scored from Daley Blind’s corners.

A third Premier League defeat before the end of September equals the total number of times Ranieri’s side lost in the league in the whole of last season.

Leicester defenders Robert Huth and Wes Morgan got themselves in a muddle at Old Trafford

Paul Pogba is starting to find his feet back at Old Trafford

The young Frenchman has understandably come under intense scrutiny since United paid a world record £89m to bring him back. He was signed to be a game-changer for Jose Mourinho and up until now he hasn’t been able to change games.

Against Leicester, we saw a big improvement. Freed from defensive duties to a greater extent, Pogba got forward to cause Leicester all sorts of problems. He was involved in the build-up to the first and second goals, and headed the fourth himself. Of course, he can get better. But for those people starting to worry that United had wasted their money, here was evidence that he can live up to the price tag.

Pogba opened his account for Manchester United and is growing into his role in the team

Louis van Gaal's fingerprints may not be so hard to wipe away after all

Mourinho repeated after this win that he has to erase his predecessor’s much-vaunted ‘philosophy’ before he can truly make his own mark on United.

‘Me and Mr Van Gaal see football in a different way,’ said Mourinho. ‘In the players’ football brains there is still a contradiction in what I want them to do.’

The truth is that three of his starting line-up didn’t even play under Van Gaal, and there was a fluency and verve to United that was sadly lacking under the Dutchman.

United were enterprising and exciting. Sir Alex Ferguson, watching from the stands, would have been impressed. They look a lot further down the line than Mourinho might suggest.