Pace and width had been part of Ferguson's DNA for 26 years, but in keeping alive his hopes of a 13th Premier League title, the Scot conceded he had to change something.

"Using the diamond does mean that a winger may be sacrificed but the game is changing," he said. "You have to have width but you do not necessarily need wingers to provide it.

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"It could come from full-backs or perhaps players such as Robin van Persie, Danny Welbeck or Javier Hernandez pulling wide.

"And of course if the manager feels the opposition has a full-back who is a poor player or is struggling then he can introduce a winger."

Ander Herrera heads Manchester United in front after 31 minutes

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Those words came to mind on Monday night, as United produced the perfect game plan to knock the holders Chelsea out of the FA Cup.

There was no Cristiano Ronaldo, Andrei Kanchelskis or Nani to take full advantage of Marcos Alonso's clear deficiencies as a left-back, but after been forced to move away from his preferred formation due to the absence of key personnel, Ole Gunnar Solskjaer has found his diamond.

Wayne Rooney was the jewel in Ferguson's crown during United's last title success, but in every department there has been improvement under Solskjaer.

There were stand-out performers throughout the side, from Chris Smalling at the heart of the defence, the courage shown by Luke Shaw and Sergio Romero in colliding with one another in the second period to deny Chelsea a sniff of a comeback, right through to the ever-willing runs of Marcus Rashford and Romelu Lukaku.

Inside the final 30 minutes, Eden Hazard chopped inside but Victor Lindelof wouldn't be beaten, throwing his body at the Belgian's shot to deflect it over the bar and preserve United's two-goal lead.

Eden Hazard was kept subdued after a lively start at Stamford Bridge

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This was meant to be the end of the honeymoon period for Solskjaer and United.

Paris Saint-Germain had delivered a reality check.

Six days ago, United were unable to handle the double blow of losing Jesse Lingard and Anthony Martial before the start of the second half against Thomas Tuchel's side.

Two goals in quick succession from Presnel Kimpembe and Kylian Mbappe was capped by the sight of Paul Pogba trudging off early having caught Dani Alves at Old Trafford.

And while the size of the task facing Solskjaer at the Parc des Princes on March 6 may prove insurmountable in the absence of three of his best performers since the start of his tenure, the Norwegian has provided an emphatic response to that setback.

In defeating Cardiff, Huddersfield, Bournemouth, Newcastle and Reading in his first five games, the jury was still out over the interim boss - but Tottenham and Arsenal were then dispatched away from home.

The defeat to PSG last week represented the first blip under Ole Gunnar Solskjaer

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Having suffered the first defeat in 12 games in charge, being faced with an FA Cup tie with Chelsea at Stamford Bridge without Martial and Lingard looked daunting.

But while the far more experienced Maurizio Sarri continued to demonstrate an inability to move away from a rigid 4-3-3 formation, Solskjaer again showed his tactical nous.

United's hopes of a 13th FA Cup title had been ended by Chelsea in each of the last two seasons, but in reaching the quarter-finals, Solskjaer produced the finest and most necessary result of his time in charge.

There has always been the promise of depth in this United squad, an embarrassment of riches that still caters for the continued struggles of Alexis Sanchez, rightly benched on Monday night.

In his place, Juan Mata took his opportunity on his return to familiar surroundings, but it was Pogba, of course, who would have the decisive impact.

Paul Pogba spoke of the trust between manager and the players after the Chelsea victory

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It was his inviting cross just after the half-hour mark that was met by the stooping header of Ander Herrera.

Mata and Lukaku were involved before the Frenchman, so peripheral until that point, picked out another one of his glorious balls, arching over David Luiz.

Herrera wasn't put off by the bobbing bed of hair nor the presence of Alonso as he guided the ball back from where it came, beyond the static Kepa Arrizabalaga and into the bottom corner.

It was here at Stamford Bridge two years ago when Herrera was sent off to change the complexion of a similarly absorbing contest after 35 minutes.

Jose Mourinho, on his first return to Chelsea as United manager said afterwards: "We all saw the game. We can all have different perspectives but I think we all have to agree there was a match until the moment when Herrera saw the red card and there is a match after that.

"Before that I saw a game with the feeling I was going to win it because everything was under control. The situation was evident because they couldn't play the way they always play. But with ten men it was very difficult for us because our strategy was to play with two players up front."

Herrera was sent off two years ago - and Jose Mourinho was unable to avoid an FA Cup exit

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The man on the end of Mourinho's criticism that day was Michael Oliver, but under Solskjaer, Herrera has been allowed to be more proactive.

He had previous success in man-marking Eden Hazard, scoring in a 2-0 win for United that merely delayed Chelsea's march to the Premier League title that same season in 2017.

Here, Herrera had Chelsea running in the opposite direction, and the first goal in this encounter always felt like it would decide the outcome.

Chelsea needed a quick reaction desperately, but they retreated within themselves. Smalling controlled the United defence and thwarted the darting runs of Hazard and with it, Chelsea's entire threat.

Marcus Rashford had the beating of Marcos Alonso on Monday night

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The game was perfectly set up for United to pick Chelsea off on the break, and having laid on Herrera's opener, Pogba was now in the mood, motoring through the gears after putting Rashford down the wing.

There, he waited for his team-mate to arrive in the box and swung in a delivery that was Beckham-esque in between Antonio Rudiger and Cesar Azpilicueta, finding Pogba eight yards out to dive onto the ball and head it into the bottom corner via the weak right hand of Kepa.

"His ball has burst at the moment, Sarriball," said Martin Keown on co-commentary duty for BBC. All the singing came from the Shed End.

Chelsea couldn't even get the kick-off right for the start of the second half, being forced by referee Kevin Friend to re-start with Alonso nearly at the United penalty area before the ball was rolled back by Hazard.

Chelsea huffed and puffed, but Sergio Romero was never unduly troubled as United supporters mocked their counterparts chanting about John Terry’s crucial slip during the Champions League final penalty shootout of 2008.

When Willian’s free-kick sailed over the bar with 20 minutes remaining, Mateo Kovacic was replaced by Ross Barkley (again).

Mateo Kovacic was ineffectual and once more replaced by Ross Barkley

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Both sightings brought sighs from the majority inside the stadium. There was the 5-0 dismantling of Huddersfield, but Sarri has appeared out of ideas for some time, even withstanding the arrival of Gonzalo Higuain, desperately quiet here.

Into the final 10, and there were more boos from the Chelsea fans as Davide Zappacosta replaced Azpilicueta. These are desperate times for Sarri, Callum Hudson-Odoi again relegated to a bench-warming role.

Prior to the game, Chelsea captain Azpilicueta had admitted that the next five matches would define the club's entire season. But he was sat on the bench come the end, as Sarri bellowed out his final forlorn instructions. Nobody was listening by then.

Azpilicueta had spoken of the inconsistencies that have plagued Chelsea's season, and if this is 'make or break' for Sarri, you would not have sensed it from the opening 45 minutes.

Cesar Azpilicueta is beaten in the air by Pogba for United's second

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United were by far the better side, with Marcus Rashford very nearly being found by Romelu Lukaku inside 90 seconds, denied by the outstretched boot of David Luiz at the near post.

Lukaku was then found by Rashford who tried to wrap his shot on the volley around Luiz but the Belgian could only find the Matthew Harding Stand.

United continue to look bright with Rashford running through Mateo Kovacic on his way to finding Nemanja Matic, and the Serbian's measured pass was headed by the advanced Chris Smalling into the gloves of Kepa Arrizabalaga.

After United finally made their dominance count, they spoiled and engaged with Chelsea’s attempts to build pressure, easing through the second 45 minutes to book a date in the last eight.

"They're like streetfighters, these Manchester United players. Alexis Sanchez has come on and he's picked up the pace of this game straightaway."

Beleif has returned to Manchester United fans since Solskjaer's arrival

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“Get back Mourinho,” came the ironic chants from the away end, swiftly followed by “Ole, Ole, Ole, Ole!” This was such an assured display, each man in red working for one another in front of the watching Ferguson, who beamed in stoppage time with his smartphone in hand.

It was meme-worthy, a text message reading, 'Shall we appoint him now?' perhaps unlikely, but Solskjaer continues to defy those who view him as under-qualified.

David Moyes, Louis van Gaal and Mourinho all struggled in the shadow of United’s great former manager, but Solskjaer has relished receiving Ferguson's shrewd input and universal influence.

A delighted Sir Alex Ferguson checks his phone with the victory secured

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So often the club's executive vice-chairman Ed Woodward has been seen with steam coming out his ears at this ground, but he stood chewing his gum as he left this part of West London delighted by the latest show of spirit and unity under the interim boss.

Solskjaer has emphatically answered those lingering questions after the PSG defeat, and the ramifications of this success both on United and their direct rivals for a Champions League place may just prove pivotal.

Solskjaer has shown in the absence of Lingard and Martial, he has a system for every occasion. Where Chelsea lacked a spark, United’s diamond sparkled every bit as it did at the end of the Ferguson era.

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