Marcus Rashford's 17th goal of the season kept Manchester United's Carabao Cup hopes alive after Manchester City had threatened to end their Wembley dreams in the first leg of their semi-final.
Rashford 70'
B. Silva 17', Mahrez 32', Pereira OG 39'
Pep Guardiola's defending champions were coasting at 3-0 with 20 minutes to go thanks to Bernardo Silva, Riyad Mahrez and an Andreas Pereira own goal after embarrassing their hosts with a display of dominant, mercurial football at Old Trafford.
However, one lapse allowed Rashford to score the goal which made it 3-1 to give them a chance in three weeks' time, having won at the Etihad barely a month ago in the league.
A bullish Ole Gunnar Solskjaer had said pre-match they still thought they were the biggest club in the world but this performance showed just how far they were from that.
His City counterpart's decision to leave his two recognised strikers on the bench and start Silva as a false nine raised a few eyebrows but it soon became apparent this was to be one of those Guardiola masterclasses.
It was a performance reminiscent of his Barcelona in their pomp, when Lionel Messi was given the freedom of the Nou Camp to orchestrate proceedings from anywhere on the pitch.
In 45 minutes Silva scored one and had a hand in the other two as he roamed freely, meaning City's forward line resembled an expensively assembled carousel as Raheem Sterling, Mahrez and Kevin De Bruyne all rotated in the central role, leaving United's centre-backs Phil Jones and Victor Lindelof chasing shadows.
The fact they often had no one to mark left them alone with their thoughts and the dilemma of whether to stay or go to and find an opponent but while they pondered that City ran riot.
United actually began the brightest with Rashford racing past a statuesque Nicolas Otamendi only for his cross to be cleared by Fernandinho, who could have conceded a penalty moments later had the United forward opted to go down under his challenge rather than stay on his feet and settle for a corner.
But in an instant the match, and effectively the tie, changed in an instant. Out of nowhere Silva fired one into the top corner off the underside of the crossbar from 20 yards and City never looked back.
United, however, were in danger of getting whiplash as they tried to comprehend the whirl of blue shirts which buzzed around them.
Silva, dropping deep on the right, turned creator as his exquisite through ball invited Mahrez to run through the middle, and although Lindelof should have done better in cutting it out, the Algeria international calmly rounded David De Gea and rolled the ball into an empty net.
The third goal was a classic counter-attack as when United lost possession on edge of City's box Silva picked out Mahrez, who in turn found De Bruyne.
Jones, starting his first match since being hooked at half-time against Sheffield United in November after injury ruled out Harry Maguire, was ignominiously put on his backside by the Belgium midfielder, whose shot was diverted by De Gea into the path of Pereira, who could not stop the ball rebounding over the line.
"Ole Gunnar Solskjaer, we want you to stay" was one of the kinder chants from the visiting City fans.
It was a tough watch for former United team-mates Wayne Rooney, Nicky Butt and Ryan Giggs, sitting together in the directors' box, but much more enjoyable for City's Oleksandr Zinchenko watching in the away end.
City had other first-half chances for Silva and Sterling while United's 'best' effort saw Mason Greenwood bundle a shot wide.
United offered slightly more forward motion after the break and were rewarded with Rashford's 70th-minute goal when Rodri lost possession on halfway and the England striker ran through the inside-right channel and stroked a shot across Claudio Bravo.
City suffered another blow when De Bruyne was forced off after being laid out in an aerial collision with Lindelof and things could have been worse, with Bravo allowing Rashford's long-range shot to slip through his grasp with the ball dropping wide of a post.
United somehow dodged a bullet with their second-half performance but still have plenty to do if they are to turn things around.
By Tom Carnduff
An easy evening for City, but they'll be a tad annoyed that they didn't add to their lead in the second-half.
Rashford got one back from United but the scoreline doesn't really reflect how poor they were this evening.
City got the job done in the first-half and taking their foot off the gas allowed United a way back into the contest.
We've got another three minutes to play at Old Trafford.
The City defence back off and give Rashford the time to unleash an effort from distance. It's a powerful strike which Bravo stops but only at the expense of a corner.
Foden replaces Mahrez in another late change by City.
He takes too long on the throw-in and Mike Dean shows him the yellow card.
Anthony Martial is on for United, he replaces Mason Greenwood.
He takes a knock and De Bruyne is off, although looks fine as he goes to the bench. Gabriel Jesus is on in his place.
The United youngster is carded after he goes in late on Mahrez as both jump to win the ball in the air.
Well, City almost had the perfect response.
Sterling is played in and picks up the ball inside the area. De Gea is out quick and the United defence look to close off any shooting lanes from a tight angle.
He elects to loft the ball over to Mahrez at the edge of the area and his first-time effort is saved again by the United stopper.
Their first real chance to score and Rashford makes no mistake!
He's played in by Greenwood and his touch takes it away from Otamendi. He fires it low into the bottom corner past a helpless Bravo. Game on? Who knows...
United line up to block Mahrez's left-side but it leaves a big gap on his right as he drives into the box. He drills a low shot towards goal but De Gea gets down to save with his leg.
And from the resulting free-kick, Rashford hits it over.
I think Ole's recognised James' problems tonight, he's been poor and looks to be sulking as he heads to the bench. Angel Gomes is on in his place.
Wow, have we just witnessed Manchester United attacking with some purpose?
Pereira picks the ball up in midfield and gets past Rodri using his pace. The City midfielder brings him down and Mike Dean shows him the card.
Just don't mention tactical fouls in front of Pep...
A late challenge on Otamendi moments ago is followed by shoving the City defender into Claudio Bravo when the goalkeeper slid out to claim the ball.
He needs to be careful. He's also 4/1 with Sky Bet to be shown a card in this game.
It was from a tight angle, a very tight angle actually, but Mahrez comes close to grabbing another.
His corner is initially cleared but it's fired back into the box by Mendy. Mahrez picks it up at the side of the area closest to where he took the corner and unleashes a shot but it's off the outside of the post.
De Gea had that one covered.
A silly challenge from the United midfielder on Bernardo Silva. Mike Dean shows him the yellow on halfway.
United have been slightly better during the opening exchanges of the second-half. If we're being honest though they couldn't be any worse.
They're trying to press City but it's just not working. The visitors are finding the gaps to get in behind when United look to close them down. We're starting to see it again in this half.
Matic is on at the break, he replaces Lingard.
More ruthless football from City? You certainly wouldn't back against it based on that first 45 minutes.
Wow, this is far too easy for City...
Bernardo Silva's thunderstrike opened the scoring before Mahrez and a Pereira own goal put them in a commanding position at the break.
This feels like a new low for United, who are just miles below the level of their opponents. They can count themselves lucky it's not at least five at the break.
Oh dear!
Mahrez is the latest to find the City forward with a pass. He tries the first-time shot from inside the area but ends up kicking it against his own feet!
He could have had a hat-trick in this first-half...
Wow, City are tearing United apart here...
De Bruyne hits a powerful cross into the area for Sterling to run onto, he slides into it but can only knock the ball wide. A tough one but he's done well enough to get something away there.
Ruthless from the visitors. It's worth mentioning we'll have a VAR check though...
City counter attack once again. De Bruyne turns Jones inside out in the area and unleashes a close range shot at De Gea. He saves it but it strikes Pereira and goes into the United net. Little the United man could do about that.
VAR check over...goal given.
United actually find themselves in City's box! The ball falls to the feet of Greenwood at the edge of the area but it's a poor effort that goes well wide with little power. Can United find a way back into this one?
Mike Dean's first real involvement of the evening. He shows Lingard a yellow for leaving a foot in on Fernandinho as the City man knocked the ball down the pitch.
Mahrez finishes off a counter attack move from the visitors.
Bernardo Silva turns provider as his through ball is inch perfect to beat Lindelof. Mahrez picks it up at the edge of the area and rounds De Gea, making no mistake as he taps it into the empty net.
City are so much better than United this evening.
Mahrez makes it two!
Sterling comes so close to grabbing City's second.
United's pressing doesn't work and City find a way past it. Neat link-up play down the right sees Walker played into the box. He elects to cut it back but Sterling's shot is straight at Lindelof and his follow-up attempt is blocked.
Far too easy for the visitors there.
...and what an effort it was!
Silva's strike is one of those that gets you out of your seat. De Gea is completely helpless as it flies into the top corner. Sublime stuff from the visitors.
Bernardo Silva! WHAT A HIT!
The City man picks up the ball 25 yards out, he drifts in and unleashes a fierce left-footed effort into the top corner. A wonderful strike!
City enjoyed the better of the early possession but United are getting into this one now and using that pace that caused City so many problems when these two sides met in the league.
That said, we're still waiting for the first real chance of the contest.
Not much to report from the opening exchanges of this one. It looks like De Bruyne is playing in that number nine role this evening, something a bit different from Guardiola!
We're underway at Old Trafford!
As Paul Higham writes...
"City also have revenge on their minds after United went to the Etihad and beat them 2-1 in a classic smash-and-grab on the counter attack. United managed just 28 percent possession that day but could have won by more as CIty left themselves open at the back time and time again.
"Despite this game being at Old Trafford, United will again operate in the same style and sit back, looking to spring forward with pace in behind City's defence - which remains their huge weakness.
"United actually hold a 5-4 record in the last 11 Manchester derby games, and the Red Devils have certainly got a better record against the better sides this season. They're unbeaten against top eight teams and have won at Chelsea in the Carabao Cup.
"Harry Maguire is a big doubt with injury though, and he'd be a big miss for the hosts who are already a massive price at around 4/1 to win the game, and almost 3/1 just to get a draw. That's a big price considering this is just the first leg."
Starting XI: Bravo, Walker, Otamendi, Fernandinho (C), Mendy, Rodrigo, Gundogan, Mahrez, De Bruyne, Bernardo, Sterling.
Subs: Ederson, Jesus, Aguero, Silva, Cancelo, Foden, Garcia.
Starting XI: De Gea, Wan-Bissaka, Jones, Lindelof, Williams, Fred, Pereira, James, Lingard, Rashford (C), Greenwood.
Subs: Romero, Dalot, Matic, Chong, Gomes, Mata, Martial.
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Odds correct at time stated