Bernardo Silva thumps into top corner from 25 yards & slips in Mahrez for second before Pereira own goal
Rashford finishes breakaway for Man Utd response
Man City and Man Utd won the last four EFL Cups between them
Second leg on 29 January - winners play Villa or Leicester at Wembley
Man Utd 0-3 Man City
Robbie Savage
Ex-Wales midfielder on BBC Radio 5 Live
It's all come from Daniel James' needless flick.
City! Wow! How good have they been!
United want half-time to come. They've missed Harry Maguire at the back, but the midfield players have not tracked the runners.
Manchester United 0-3 Manchester City
Grim faces in the stands. United fans may have expected a tough test tonight but they are getting a schooling out there.
Andreas Pereira (OG)
Kevin de Bruyne v Phil Jones - it's just not fair really.
Manchester United lose the ball high up the pitch and they are bang in trouble against this lightning Manchester City attack. City have four men streaking down the middle, Brandon Williams does really well to make a challenge but the ball ends up at De Bruyne's feet.
He runs at Jones, squares him up and then puts him on his backside with a bodyswerve. David de Gea saves De Bruyne's shot but the ball cannons out, hits Andreas Pereira and flies in.
There's a second leg to come remember...
Image source, Rex Features#bbcfootball or text us on 81111 (UK Only)
KN: Awful from the minute City cleared the corner. Williams had no-one to pass to for about 5 seconds. Then Lindelof made two bad mistakes in 30 seconds and it’s no more than City deserves
Dave Payn: Port Vale put up a bigger fight against City
Shuga: Just a reminder that Man Utd have not scored a goal this Decade.
Manchester United 0-2 Manchester City
Better from the hosts as Mason Greenwood engineers a shooting chance on the edge of the area, he snaps a shot off with his left foot but it's not a clean connection at all.
Man Utd 0-2 Man City
Simon Stone
BBC Sport at Old Trafford
Ole Gunnar Solskjaer just marched back to his seat looking very grim faced.
Manchester United made a bright start but now they are being overrun in midfield.
Unless something changes quickly, they have zero chance of reaching the final and are heading for a morale sapping defeat.
Man Utd 0-2 Man City
Robbie Savage
Ex-Wales midfielder on BBC Radio 5 Live
It's absolutely magnificent. Victor Lindelof slides in and goes to ground. David de Gea makes Riyad Mahrez's mind up for him by coming out from goal.
Brilliant tactics from Pep Guardiola - a masterclass from Pep Guardiola.
Manchester United 0-2 Manchester City
When did Manchester City even have time to work on this new, strikerless system? It is working a treat. The man in possession has so many quality options on every time.
Riyad Mahrez
Bernardo Silva, c'est magnifique.
He's got a goal already and now the Portuguese picks up a header from Victor Lindelof, dances past one challenge and then plays a peach of a through-ball in behind Lindelof. He slides in desperation but can only toe the ball into Riyad Mahrez's stride.
Mahrez arrives into the area at full speed, David de Gea is betwixt and between, Mahrez glides around him and taps it in.
Made that look easy.
Image source, ReutersManchester United 0-1 Manchester City
That is better. Fred struggles to take a corner as the wind whips through that corner of Old Trafford, twice the ball runs away from him. The ball is then whipped in brilliantly by Andreas Pereira but there's nobody there.
Man Utd 0-1 Man City
Chris Bevan
BBC Sport at Old Trafford
The Stretford End has been trying to get United playing, doing that thing where they repeatedly chant 'Red Army' quite quietly at first and it feels like the whole ground ends up singing it as they build up momentum.
In the past that was matched on the field as the United team built up a head of steam, but that part is yet to happen - Ole Gunnar Solskjaer's side are struggling to string any passes together at the moment and are not posing much of a threat.
Man Utd 0-1 Man City
Robbie Savage
Ex-Wales midfielder on BBC Radio 5 Live
You can see now Ole Gunnar Solskjaer and assistant Michael Carrick staring into space in the dugout - they need to do something tactically.
If City get another then it's all over. I can't see United going to the Etihad and getting something.
Manchester United 0-1 Manchester City
Manchester United haven't had a shot on target yet, they didn't have any against Wolves either. They have won a corner though as Daniel James makes ground up down the right.
#bbcfootball or text us on 81111 (UK Only)
Utd gone behind at home against a City side who are so unconcerned about them they're playing without a striker. OGS has 7 games in next 23 days and the silence around Pochettino is deafening.
Frank, Cwmbran
Worth pointing out that Giggs, Butt and Rooney have been in the box longer tonight than United's front three.... Would give anything for another Rooney moment against City
Paul J, Newmarket.
Manchester United 0-1 Manchester City
Mesmeric as Manchester City keep the ball for getting on for two or three minutes. United are getting a chasing.
Man Utd 0-1 Man City
Chris Bevan
BBC Sport at Old Trafford
Groans from the Stretford end as United surrender possession cheaply again.
Meanwhile, City's supporters are singing about being the "pride of Manchester".
Both sets of fans have had very different nights so far. Still, it's early days.
Manchester United 0-1 Manchester City
This is a bit like the highly anticipated Year 10 v Year 11 end of term game at my high school at times. A different level. Kyle Walker and Kevin de Bruyne play a one-two and just go up two gears, burning past men in red at a speed they just can't compute.
Walker cuts the ball back, Raheem Sterling gets a shot away which is well blocked, he then shoots again and Victor Lindelof does well to charge that one down as well.
Manchester United 0-1 Manchester City
Bernardo Silva goes past two United men in midfield with ease, travelling nicely at speed. Jesse Lingard gets a good recovery tackle in but Silva then hits the iron cranium of Phil Jones, accidentally, and needs a moment to regather his thoughts.
He's OK.
Manchester United 0-1 Manchester City
Riyad Mahrez with a Phil Neville stepover to chop in from the right, he looks to repeat the Bernardo Silva incident but this time he's shut down. City are buzzing at the moment in this game.
Man Utd 0-1 Man City
Simon Stone
BBC Sport at Old Trafford
Bernardo Silva dropped into a little pocket of space then to receive what appeared to be an innocuous square pass from Kyle Walker.
No-one from United was alive to the danger and although Fred tried to get across, Bernardo had too much space to deliver the killer blow.
The question for the hosts now is do they push forward looking to equalise or catch their breath a little bit. It is a big problem.
Image source, Getty Images