Tom in Durham: With all the talk of Manchester City falling so far behind Chelsea, it might be forgotten that should they lose today, City will only be four points ahead of Liverpool in fifth (if Liverpool win their game in hand against a terrible Newcastle side on Monday). Unthinkable?

Alex in Norwich: Good result so far for Utd but Van Gaal a genius? Spending £59.7 million on Angel Di Maria only to warm the bench. It may have worked in this game so far, but it's about a fiscally prudent as letting Greece run your bank account!

Ashley in Salisbury: City need to come out looking for a fight in the second half, Manuel Pellegrini can no longer inspire the players like that. He needs to go.

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Confirmation that Yaya Toure is now City's captain. Vincent Kompany is off, Eliaquim Mangala on. Can he beat Marouane Fellaini in the air?

Image source, Reuters

Here come the sides out of the tunnel, huge ovation from the home fans.

Vincent Kompany is indeed coming off at half-time. We believe he injured his thigh when fouling Daley Blind.

The debate over whether Vincent Kompany should have been sent off will rage on, but he may well be coming off anyway. Eliaquim Mangala is going through a long and intensive warm-up at half-time.

Image source, AFP/GETTY

I count that five times that Phil Jones has a look at Sergio Aguero before Aguero put City ahead - yet he still seemed surprised that the Argentine was behind him for a tap-in!

Jeffrey James: Credit to the United players for not making a big deal about that Kompany challenge. Could've been off.

Khan Karn: Never ever a red for Kompany, 20-years-old ago that wouldn't be a yellow. one legged tackle, no booking for me and I'm not a fan of City.

Senn Ranson: Don't think Kompany's challenge was a red. Besides, don't want City to have an excuse at full-time. United lead deserved.

Manchester City have not won any of the last 86 Premier League away games where they've trailed at half-time, last winning in April 1995.

That is ridiculous.

Earlier today we put some of your questions to BBC pundit Kevin Kilbane.

Check our the BBC Sport Facebook, external page for Kevin's answer on a wide range of subjects, including his tip for manager of the year, Arsenal's recent form and the promotion prospects of his former club Preston.

If the scores were to stay like this, City would be 12 points behind Chelsea and lodged in fourth place. United would go four points above them and just one behind Arsenal.

Image source, Getty Images

Liverpool striker Mario Balotelli reacted to Sergio Aguero opening the scoring at Old Trafford by tweeting. I imagine he's had to turn off his notifications now...

Image source, Twitter

BBC Sport pundit Robbie Savage at Old Trafford

"Great start by City and they deserved a goal, but United have been in control ever since. Vincent Kompany's been lucky to get a yellow card - it was excessive force and out of control. It ticks a few boxes for what you would consider a sending off."

Phil McNulty
BBC Sport chief football writer

"Manchester City came out trying to deliver the quick knockout but Manchester United stayed on their feet despite that early setback and now have that lead to protect. A superb game helped by some poor defending. Plenty more where this came from you suspect."

Chris Mitchell: Poor challenge and equally poor decision from Mark Clattenburg and his assistant. Reckless and out of control. Lucky boy Vincent Kompany.

Ade Williams: Vincent Kompany has been VERY lucky there.....VERY lucky!

Callum Anderson: City beginning to lose their composure - characterised by Kompany's tackle on Daley Blind.

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And breathe...

Richard Clarke: The 'genius of van Gaal' as Simon from York puts it, is to recognise Moyes' signings are better than his.

Richard obviously has a few issues with Simon's thoughts - see the comments after 25 minutes.

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Well played Phil Jones. He does really well to tackle Sergio Aguero as he tried to dart around him, and then starts a counter attack which is almost ended by Marouane Fellaini.

He dives on to Antonio Valencia's cross but brave defending from Pablo Zabaleta knocks it clear.

TWO MINUTES added on to an enthralling half. High in entertainment if not quality.

BBC Sport pundit Robbie Savage at Old Trafford

"Oooof. It was a lunge in from Vincent Kompany, a rash challenge. You have to say that is a borderline because his studs are up, he's caught him high up but the referee has probably just about got it right."

Vincent Kompany is worried. Referee Mark Clattenburg takes a long, long time to decide whether his lunge on Daley Blind is a reckless one and after consultation with his linesman goes for a yellow card.

Kompany thought he was off there. It wasn't a great challenge, his foot was high. Did City get lucky there?

Image source, AP