Alejandro Garnacho's stunning overhead kick was the highlight of the game at Goodison Park but Mainoo's display in central midfield was another huge positive for Erik ten Hag's side.

The 18-year-old academy product was thrust into the starting line-up for his first Premier League start having only previously featured as a late substitute against Leicester in February.

He made a vital goal-line clearance to keep Manchester United in front after Garnacho's goal and earned widespread plaudits for his performance both in and out of possession.

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"There's an 18-year-old out there who looks more composed than anyone," said Neville on co-commentary during the game.

"Mainoo has been Manchester United's best player by a street. A brilliant, brilliant Premier League debut from him."

Neville gave the player-of-the-match award to Garnacho for his amazing opening goal but felt Mainoo was the "standout performer".

Fellow Sky Sports pundit Keane agreed. "Unbelievable," he said. "We don't want to get too carried away but I'm sure we will.

"He looked like he always had time on the ball today, his decision-making, in terms of when to go long when to go short, in terms of off the ball as well. What an all-round performance.

"The club obviously think highly of him. With the build-up to the game today, coming to Everton, for the manager to put him in, he and the staff around the place obviously must trust him.

"Good luck to the kid. He was outstanding. It's a great start for him. Let's hope he stays injury-free and gets a run of games for Man Utd because he looked a Man Utd type of player.

"Nice and brave, lots of courage. I loved watching him."

Erik ten Hag was similarly impressed, hinting that he would have given the youngster a chance sooner this season had it not been for an injury he suffered during pre-season.

"He has a lot of abilities," said the Manchester United boss in his post-match press conference.

"It was a really disappointing moment in pre-season when he got a bad injury, for him and also for our team because I know he can progress a lot if he plays as he did today. I know young players can develop quickly.

"We thought it was the moment to bring him in. He did a great job. Now he has to build on this."

Back in the Sky Sports studio, Karen Carney added: "He was just really, really composed.

"He was brave and kept things nice and steady and tidy, one and two touches.

"That holding midfield position is so vital. For an 18-year-old to come here under the pressure they thought they might be under and just glide past players…

Sometimes he held onto it a little bit too long. Maybe it was a bit like, 'You're not playing for the youth team now, you might get caught.' But I thought it was a fantastic performance from a young man who has got a bright future ahead of him."

Former defender Michael Dawson said: "I thought he started every attack. The two centre-backs split and he slotted in.

"He got on the half-turn, he played everything easy, and when he had to make a hard pass, he did.

"They must think highly of him because Sofyan Amrabat was on the bench. I thought it was an all-round magnificent performance and he should be really, really proud today."

Neville: Mainoo looked like a Man City player!

Sky Sports' Gary Neville speaking on the Gary Neville Podcast:

"It was impressive. There's no point in getting carried away, he's got 17 or 18 years in front of him with a lot of work to do.

"But sometimes, when you see a player come in for the first time, the temperament, he's obviously got technical ability and skill or he wouldn't be playing for Man Utd or getting picked by Erik ten Hag.

"What you don't know is how they'll handle it - and he's gone in there at Goodison Park, in what could've been the most ferocious atmosphere here for many years - and he looked class.

"We know he's got class, but he looked class in that environment. I always judge players when it's the most difficult part of the game. And when they had that period in the first half, he was the only one who showed up and looked himself.

"The biggest compliment I can pay him, and it hurts to say this is that he looked like a Manchester City player. I was thinking he was someone Pep Guardiola would look at and think he'd want him in his midfield."

Analysis: Mainoo made an instant impression

Sky Sports' Adam Bate at Goodison Park:

The on-air player of the match award went to Alejandro Garnacho given his remarkable goal, but Manchester United supporters will be equally enthused by Kobbie Mainoo's first Premier League start as their team won 3-0 away to Everton.

It was astonishing how composed he looked in the middle of the pitch.

It was instant too. On an occasion when the febrile atmosphere at Goodison Park had many wondering whether Manchester United would be able to cope, he found time and space where there should have been none, unafraid to put his foot on the ball.

When substituted to a warm ovation from the travelling support, Mainoo had completed 34 of his 41 passes - boasting the best passing accuracy of anyone in the United starting line-up. It was a vindication of the faith shown in him by Ten Hag, preferring him to Sofyan Amrabat.

Couple that with the defensive work that he did, most notably clearing the ball off the goal-line when it appeared that Dwight McNeil had forced home the equaliser, and Mainoo appears to be a player who can impact the game with and without the ball.

The form and fitness of Casemiro has left a void in midfield and with Mason Mount out for the foreseeable future, a double pivot looks likely to be the preferred option. His manager now knows that he has a talented teenager ready to step into that role.