United thought they had taken a first-minute lead after a Marcus Rashford shot was saved and the rebound bounced in off a defender, but the offside flag was up - and the same happened at the other end a minute later with Ilkay Gundogan’s finished chalked off.
Kevin de Bruyne then thumped the post from range and Phil Foden raced through to score - but again the flag was correctly raised and a third would-be goal ruled out in an entertaining opening quarter of the game.
That tempo did slow thereafter, but John Stones finally opened the scoring just five minutes after the restart, knocking home from close range after a free-kick from the left found him at the far post. United occasionally threatened from range as they searched for an equaliser but Zack Steffen was rarely tested to his maximum and City sealed progression when Fernandinho fired in a second from outside the box. Here are five things we learned from the game at Old Trafford.
Upturn in tempo
Five minutes in, this was already a better derby than the turgid fare the teams served up in the Premier League recently.
Both teams had a goal ruled out and both key attacking midfielders had long-range strikes go close to scoring - the impetus and emphasis for both teams was to attack, to look for the victory.
Perhaps it’s because this was a derby, or a semi-final, but also perhaps it’s a step back toward the elite teams putting in better performances after a period over the busy Christmas and New Year schedule when every game seemed to drag and creativity seemed at a real low.
United’s attack fails to step up
Ole Gunnar Solskjaer’s side had gone seven unbeaten starting with the derby draw in December, scoring 16 goals in that time.
That’s obviously boosted somewhat by the hammering of Leeds, but it should also have been building plenty of confidence and familiarity in the front line.
All of the top talent started this game - Martial, Rashford, Pogba, Fernandes - but they rarely put much link-up play together between them, mostly just having individual and sporadic moments such as Anthony Martial’s attempted dribble into the box and Bruno Fernandes’ early shot from range.
As a unit it wasn’t good enough, as a defensive block they didn’t always do enough to stop City. Fernandes was perhaps the biggest disappointment given he is usually the biggest spark - here he was wasteful in possession and on the periphery too much.
The turnaround in form and fortunes of John Stones at Manchester City is quite remarkable this year.
Having looked fourth-choice at best even before Nathan Ake and Ruben Dias had been signed, he has somehow turned matters around to the extent he’s in the line-up on merit on a regular basis.
Here he not only defended well, as he has done so often of late, but also scored the goal which sent City into the final - both a symoblic and literal marker for how much he has reinvigorated his career at the club.
Perhaps an England recall is next.
Two stand-out performers for City were right-back Joao Cancelo and fellow Portuguese defender Ruben Dias - not for the first time recently.
The duo have settled into the side and made starting positions their own this term - albeit Cancelo switching from left to right depending on the availability of others.
The full-back has incredible delivery, great link play, is tactically intelligent and is determined in the challenge.
His new central team-mate has been aerially dominant, consistent, without any kind of hesitancy about his game - a very good signing so far.
Wembley and Spurs
Spurs’ victory on Tuesday night was routine and well-earned, so both Manchester sides already knew who would be lying in wait in the final.
Perhaps unsurprisingly, it’s a Jose Mourinho - Pep Guardiola final that we’ll now await in April, after the final was put back in the hopes of having fans inside Wembley.
The two have clashed in so many big games down the years that in truth a League Cup final isn’t the most important of them, but it will still be an occasion both seek to win with all their professional pride and unrelenting desire for success.
For Mourinho, it’s a chance to show he has turned Spurs around and secure a first trophy for them in over a decade; for Pep, it’s the chance of four in a row in this competition and a return to winning ways after being empty-handed last season.
The final is still three months away, but a tasty Wembley occasion awaits.
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