BBC Sport pundit Robbie Savage at Old Trafford

"That was wonderful defending by Valencia. If only Aguero would have looked up to see the options available to him in the middle."

Phil Jones loves a backpass - he's played more passes to his keeper than anyone else. And City should do better there!

Where was United's defence? James Milner slides Sergio Aguero down the side, there's only Antonio Valencia back for United but he manages to stop Aguero from squaring to the free David Silva.

Fine move from City as Sergio Aguero rolls his defender and finds Fernandinho, who sneaks a smart pass around the corner to James Milner. He has all sorts of space and time, but leans back and plants a horrible shot into the Stretford End.

Image source, PA

Marouane Fellaini causing more damage, bringing the ball down and finding Wayne Rooney - but the flag was up against Rooney. Someone needs to get a hold of Fellaini for City.

A gem of a pass from Yaya Toure almost has Sergio Aguero in on goal but that man David De Gea sweeps up again, David Silva is then booked for a crunching tackle on Juan Mata. Can't take your eyes off this.

Phil McNulty
BBC Sport chief football writer

"Manchester United's fans are loving this. Every tackle being cheered thunderously. They have been on the receiving end of three successive defeats to Manchester City here at Old Trafford so safe to assume they want this to be payback time - but given the standard of defending on show so far it is also safe to assume there will be more chances."

Ian Brennan: That completes the transformation of Fellaini from last year's flop, to this year's rock. Great scenes.

Paul Lummis: Clinical finish by Fellaini, who responds by celebrating in typically awkward fashion.

Brett Mills: David Moyes signings are having the biggest impact on Man Utd's changing form and fortunes!

City respond well to going behind, James Milner in the thick of it again and wins a corner, which Martin Demichelis heads comfortably wide.

Marouane Fellaini - as Gary Lineker points out - was possibly marginally offside as he headed United ahead. But if he was, it was incredibly marginal.

Match of the Day presenter Gary Lineker

Image source, Twitter

A goal and an assist for Ashley Young, a goal for Marouane Fellaini, while Angel Di Maria and Radamel Falcao sit it out on the bench.

Kleberson and Eric Djemba-Djemba are coming back in the summer.

BBC Sport pundit Robbie Savage at Old Trafford

"I said before the game that Fellaini would be the key man in the match. It's a great ball from Ashley Young and he's got his head where it matters. Joe Hart got a hand on it but he couldn't keep it."

Image source, Getty Images

Manchester City's defensive frailties exposed again as United come from behind to lead! Daley Blind backheels to Ashley Young, his cross is superb and Marouane Fellaini is free to thump in a header.

I mentioned earlier that he could be a weapon against the City defence. And he has been. Of mass destruction.

Image source, Reuters

Yaya Toure rolls away from Chris Smalling with a lovely touch but he doesn't get a free-kick as he falls to the ground. The early break-neck speed of the game has subsided slightly now.

Simon in York: Is anyone still doubting Van Gaal's genius? He's taken Ashley Young and turned him into a truly elite forward capable of keeping the likes of Angel Di Maria out the side. He has the managerial Midas touch.

Andy in Armagh: Absolutely crucial for Manchester United to hit back so soon after falling behind. Hopefully this will spark them into life. Game on!

James: Man City will not be winning the league this season but to finish below United would be to much to bear. City really up for this.

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James Milner is the first man in the book for a cynical check on Ander Herrera. A definite booking. Interestingly Wayne Rooney has only had six touches in the first quarter of the game - the fewest of any outfield player.

David De Gea off his line again, racing out to clear away from James Milner who was in behind the United backline. Milner is basically playing up front.

Gael Clichy bombs on down the City left and whips in an early cross, Sergio Aguero is well blocked and David Silva can't get a shot away in the aftermath. End-to-end stuff. Jose Mourinho would hate this. No control in midfield at all.

David De Gea deals with a dodgy backpass brilliantly and in fact starts another United attack down their left, but Daley Blind runs out of room. The first 20 minutes have flown by.

Phil McNulty
BBC Sport chief football writer

"What a start. Manchester United needed to strike a blow as they came under siege and it came from Ashley Young. City have not taken a backward step and the atmosphere inside Old Trafford is deafening. More goals in this surely."