For the first time this century, Manchester United conceded three first-half goals at Old Trafford. They were fortunate it wasn’t more.
Out-thought and outclassed by Pep Guardiola's Manchester City, the hosts were given a painful reminder of just how far they have fallen behind their cross-town rivals.
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Indeed, the Catalan coach masterminded a dominant and devastating 45 minutes of football that embarrassed United in their own backyard.
United may have restored some pride by pulling a goal back after the interval through Marcus Rashford but, in truth, manager Ole Gunnar Solskjaer never produced an answer to the problems Pep had posed.
City are looking to land the Carabao Cup for a third successive year. United, by contrast, appeared to be playing more in hope that expectation that they could end a three-year wait for silverware and give their noisy neighbours a bloody nose on the way.
They barely landed a blow until Rashford finished off a fine second-half breakaway, which gave them hope that a trip to the Etihad Stadium – where they have had some success in recent years – might be worth making.
However, they had already been taken apart by a Guardiola tactical masterplan that looked like it had killed the tie off by half-time in the first leg.
The former Barcelona boss resembled a chess grandmaster as he stood on the edge of the technical area, pointing and shifting his players throughout. In the home dugout, Solskjaer could only sit and watch City run rings around his players.
Guardiola was at least three steps ahead of his opposite number, and it will have been a useful footballing lesson for Wayne Rooney, back at Old Trafford as a spectator, as the United legend begins his burgeoning coaching career at Derby County.
Solskjaer’s strategy was clear: soak up the pressure and try to catch City’s slow defence on the counterattack.
It worked at the Etihad a month ago and Guardiola wasn’t going to change his philosophy of playing high up the pitch and trying to dominate possession. Only this time the City boss made small changes that that made a huge difference.
His first surprise arrived an hour before kick-off when he left his two main strikers, Sergio Aguero and Gabriel Jesus, on the bench, with Bernardo Silva and Kevin De Bruyne selected as false nines.
The energy of the two midfield dynamos was too much for United, as the pair drifted all over the pitch, playing as the furthest players forward one minute, and screening the back four the next.
Bernardo, in particular, was outstanding, producing the kind of all-action display that saw Guardiola describe him as the most effective player in the Premier League.
It was the Portuguese who opened the scoring with a stunning 17th-minute strike that flew past David De Gea form 25 yards out and he then turned provider, putting Riyad Mahrez in on goal for City's second.
The visitors' third goal was all about an outrageous feint from De Bruyne that sent Phil Jones hurtling towards the Sir Alex Ferguson stand. Unfortunately, the Belgian's subsequent shot was saved but the ball rebounded off Andreas Pereira and into the net.
A 3-0 lead was just rewarded for a classic City performance, one founded upon innovation and industry, perfectly personified by Bernardo. However, he wasn't the only player to shine.
Rodri flitted between midfield and defence to brilliant effect, shutting down United at every opportunity, Ilkay Gundogan offered intelligent control of the ball, while Kyle Walker and Benjamin Mendy surged forward incessantly from wide positions.
At the back, Fernandinho and the much-maligned Nicolas Otamendi were too wily for United's youthful attacking duo of Rashford and Mason Greenwood as the home side failed to have a shot on target in the first half.
Rashford and Greenwood did conjure a goal between them with 20 minutes to go, after Angel Gomes had stolen possession in midfield, but United never really looked like getting themselves back into the game, or indeed the tie.In last season’s semi-final first leg, City beat League One Burton Albion 9-0, rendering the return fixture irrelevant.
They could have done likewise at Old Trafford on Tuesday night. They really should have. The gulf in class was that big at times. Between both sets of players, and their respective managers.