Last Updated: 22/09/13 6:21pm
A fantastic free-kick from Rooney curls into the top corner from 30 yards, making him the all-time top scorer in Manchester derbies with 11 goals.
United hit the woodwork! Evra steals away from his marker Aguero and heads Rooney's centre towards goal - but the ball comes back off the post. The Red Devils have several subsequent half-chances too but can't turn the ball home.
Relief for De Gea. who spilled Dzeko's fierce shot from 25 yards but recovered to clutch the ball gratefully.
Smalling heads away Milner's cross after the substitute danced into the right side of the area. Then Ferdinand has to deal with another deep City delivery.
Valencia wants a penalty after tussling with Kolarov on the right flank. The United winger appeared to wait to go down until he was in the area. His protests to Webb end up getting him cautioned.
Fellaini shoots from inside the area with a curling powerful shot that almost deceives Hart, but he manages to tip the ball over. Good chance for United.
Fellaini chests down a cross in the box but Webb decides he pushed Zabaleta before doing so. The Belgian is baffled.
United win a free-kick just over 20 yards out, after a foul by Fernandinho. Rooney kicks the ball straight into the wall.
Excellent spot by Carrick, who releases Welbeck down the left channel. He comes inside and shoots from the top of the box but Nastasic deflects the shot, and Hart claims.
De Gea has to push Toure's shot round the post, as City attack down the right again and win an eighth corner of the match.
Fellaini is flagged offside as United continue to chase a goal. Around 35 minutes left of this contest, and City look happy for the time being to let the visitors have possession. Kompany heads away Evra's cross.
A boisterous atmosphere inside the Etihad now. United are on the attack - and then Rooney fires over from 10 yards. Smalling crossed in from the right, and the ball ran through to the England striker but he leaned back and his shot lacked accuracy.
Vidic rescues United from conceding a fifth as he blocks from close range just as Negredo was looking to turn home another Navas' right-wing cross.
Navas delivers a cross from the right to the back post, and with Kompany up front for this attack and drawing away the two United centre-backs, Nasri is free to volley home a fourth. City in dreamland.
Aguero lifts a cross into the area, but the ball is chested back to De Gea. Tom Cleverley is about to come on for United.
Negredo spins Vidic on the left side of the area and knocks a simple cross over for Aguero - who has not been tracked - to net his second goal of the game. All over?
Both Wayne Rooney and Matija Nastasic have to watch their steps in the second half after picking up bookings. Could the potential introduction of Chicharito trouble the Serbia centre-back? No changes in the interval for either side, however,
And feedback from City fans. Ry Ratcliffe on email: "I'm a City fan and hoping we stay in front, great RVP isn't playing or we'd be in trouble but it'll be an interesting 2nd half, one more goal would clinch it." Dr. Acula on Twitter says: "City have to guard against complacency now, I remember the Community Shield when we were 2-0 up at HT and threw it away."
Emails from United fans first. Chris Green: "If we don't start tightening up at the back, the scoreline could become embarrassing, which would be a 'big hammer blow' for all United fans." Daniel Jones: "Kagawa and Hernandez must come on second half." Neil Future: "Moyes needs to bring on Kagawa, put him in the middle, put Rooney on the left."
Let me know your thoughts on the first half! Email me at firstname.lastname@example.org or tweet me at @jonboy79. United fans - what changes should Moyes make at the interval? City fans - any fears lingering, or are you home and hosed?
Negredo wins the header from Nasri's corner, nods it down to Yaya Toure who forces the ball over the line. A crucial second goal for City just before the break.
Into one minute of added-on time in the first half. Young blocks Zabaleta's right-wing cross, for another corner...
Rooney's free-kick from a wide position on the right is headed out to Young, but his optimistic attempt to find Welbeck fails.
Valencia tries a shot from outside the area, but it's a poor effort which skims harmlessly across the face of goal. City have one shot on target from seven attempts so far; United have had just one off-target effort in the whole game.
Young curls in a high cross which Hart claims comfortably. The physical battle between Kompany and Rooney has been intense, with the City captain having the upper hand so far.
Negredo's shot from 30 yards is deflected wide. City broke quickly after Fernandinho intercepted Fellaini's attempted pass into the box.
Improving signs from United. Welbeck challenges Hart as Evra crosses from the left, giving City the chance to relieve the pressure.
Negredo teases the ball through to Aguero, but the pass is a little too heavy. The interplay between the two City strikers has been hugely impressive so far.
Ashley Young makes a crucial tackle on Navas in the area - close to being a penalty perhaps, but just the right side of fair.
Slight confusion as to why the flag went up when United were attacking down the left - the ball hit Evra on the upper chest, but then went out of play too.
Rooney is the first United player booked - he's pushed Webb too far in the first half hour, it seems. A caution by persistent accumulation of minor offences.
Superb control from Valencia to bring down Rooney's chipped pass to the right flank and move the ball past Kolarov.
Evra intercepts City's free-kick routine and the ball rolls back to De Gea. Home fans claim a passback, but Webb lets play continue.
A half-hearted penalty shout as Kolarov goes down in the area after running into Smalling. City have to make do with a corner instead.
Rooney is flagged offside as he receives Welbeck's pass in the area and tries to flick the ball over Hart. It's close, but replays show it was a correct decision.
Another tussle between Kompany and Rooney results in the latter losing his headband, much to the home crowd's delight. Webb has to calm the United striker down.
Another chance for City - Navas' cross from the right is headed down by Smalling, but Nasri picks up the loose ball ahead of Valencia and shoots just over the bar.
United win their first corner, but Rooney's delivery isn't good enough to find the heads of Fellaini or Vidic.
Poor defending from United down the right leads to the opener. Smalling is left one-on-one with Nasri, and Valencia fails to track back quickly enough as Kolarov passes his City team-mate on the overlap. He crosses from the left, and Aguero nets with a stylish volley. First blood to City.
Webb is over quickly to deal with a flashpoint between Rooney and Aguero. The United striker was snapping at his opponent's heels and then kicked the ball into him. The resulting free-kick is eventually cleared.
First 13 minutes - City have had 65% of possession. Toure's low shot from distance deflects off Vidic's heels for the hosts' third corner so far.
An ambitious long-range attempt from Kolarov is blocked, after what had been patient build-up from the hosts. Negredo does superbly to retain possession after an overhit cross.
De Gea punches Nasri's corner clear - the ball comes back to the Frenchman, who crosses in for Nastasic to head over.
Vidic has to head Kolarov's cross behind for a corner, after an intelligent leave from Negredo for Aguero.
Jeers from the home fans for a De Gea clearance which goes straight out of play. City in the ascendancy at the moment.
Negredo tries to control a high ball on the edge of the box, but ends up spooning it back to De Gea.
United win a series of throws down the left - eventually Young is released into the box, but he's strayed offside.
Nastasic and Smalling go up for a high ball, and the United player comes off worst. Webb shows Nastasic the first yellow card of the game.
Vidic passes the ball straight to Navas as United try and be a bit too clever clearing their lines. His shot from 25 yards goes over the bar.
Aguero wins a corner off Vidic after displaying some trickery on the right flank. Nasri takes it, but United defend it well and then Zabaleta sends the ball out of play.
Carrick picks out Rooney in space in midfield, and the pass goes forward to Welbeck - but he slips in the D and City regain possession.
Welbeck robs Kompany in the first 10 seconds, and thinks he's won a corner - only a goal kick though.
Gary Neville thinks the midfield battle will be key today - Michael Carrick and Marouane Fellaini up against Fernandinho and Yaya Toure.
The two teams are in the tunnel and we're almost ready to go. Howard Webb is the referee at the Etihad Stadium today.
Here's some interesting Opta stats for you ahead of kick-off... 1. Yaya Toure has made 347 passes this season - 30 more than any other player in the division, and 65 more than Utd's leading passer Michael Carrick (282). 2. Since the start of 2012/13, no side has kept more clean sheets in the Premier League than Manchester City (21). 3. United's Wayne Rooney has now either scored or assisted 40 goals in his last 44 Premier League games.
City boss Manuel Pellegrini, speaking to Sky Sports before kick-off: "We are always making some rotation - for this match, it's better for us to start with Negredo. Van Persie's a very important player for United, but they have always the same power whoever plays. For the fans, this is the most important game of the year. I always enjoy good matches - but I enjoy double if I win!"
Some more betting advice now: "Six of the last seven Premier League meetings between these two sides at the Etihad Stadium have gone under 2.5 goals and Sky Bet offer 8/11 on that outcome again. Those considering going under 2.5 goals but are unconvinced by the odds may like the look of 'no' on both teams to score at a greater price of 5/6, while City to win to nil appears to carry good value at 5/2."
Some United fans getting in touch about David Moyes' team selection: "Terrible selection by Moyes. Should have been Kagawa instead of Young and Hernandez instead of Welbeck," says Barry Lee on email from South Carolina, USA. Meanwhile, Chris Peddie writes: "Can someone please tell me why Young is starting ahead of Hernandez ? Jury still out for me on Welbeck and Young just doesn't cut it. Would have preferred to see Chicarito and Nani getting a run out today as this game would have suited them. Think Moyes has just handed City the advantage with that line up. Was optimistic for a United 3-1 win but now going for a City 2-1 victory. Really hope I'm proved wrong!"
Man City captain Vincent Kompany, speaking to Sky Sports before the match: "It's a big day for everybody in Manchester. Whatever the outcome, there's going to be some drama as always. We've done all the right things to prepare in this game."
Our friends at Sky Bet have an offer for you: "NEW PRICE BOOST! Wayne Rooney to score first v #MCFC is now 9/1! Can he replace RVP?" Click here to snap it up.
United boss David Moyes says Robin van Persie has a groin injury: "It's nothing serious. He could have a chance for Wednesday."
The away fans now. Sean McGrinder doesn't sound too confident on Twitter, to say the least: "As a UTD fan, UTD isn't going to win with Young, Welbeck on the field!!!" On email, Gareth Bull says: "Shame about RVP, Rooney is looking as hungry as ever, if he turns up today look out city, the blues do look frightening on paper. Come on the Reds"
Some of your feedback coming in via Twitter. Two City fans up first. Harry Shearsmith says: "Glad to see Negredo starting, think 2-1 City - Yaya Toure and Negredo." Meanwhile, Andrew Hartley writes: "So relieved RVP isn't playing but still gonna be really nervous! Going for a tight one-goal winner..."
What are your thoughts on the two starting line-ups today? Let me know. Email me at email@example.com or tweet me at @jonboy79.
And confirmation also that Robin van Persie will not feature for Manchester United today; meanwhile, Shinji Kagawa drops to the bench. Ben Amos is preferred to Anders Lindegaard as back-up goalkeeper. Alex Buttner, Tom Cleverley and Nani are all back among the substitutes, with Fabio and Anderson also missing out today. Phil Jones (ankle) and Rafael (hamstring) are both injured.
So confirmation there that Edin Dzeko drops to the Man City bench, while Micah Richards is fit enough to be named among the substitutes after overcoming a hamstring problem. Jack Rodwell is not included in the matchday squad today.
So that's two changes made by Moyes to the Man Utd team that started the 4-2 win over Bayer Leverkusen in the Champions League - Welbeck shakes off a knee injury and starts along with Young, with van Persie and Kagawa making way.
Man Utd starting line-up v Man City: De Gea, Smalling, Ferdinand, Vidic, Evra, Valencia, Carrick, Fellaini, Young, Welbeck, Rooney.
Shock Manchester United team news - Robin van Persie misses out for the champions due to a thigh strain.
So Manuel Pellegrini makes just one change to the Man City team that started the 3-0 win away to Viktoria Plzen in the Champions League in midweek - Negredo comes in for Dzeko. David Silva is not yet ready to return from a thigh injury, while Gael Clichy (hamstring) is missing too.
Man City starting line-up v Man Utd: Hart, Zabaleta, Kompany (c), Nastasic, Kolarov, Nasri, Fernandinho, Toure, Navas, Aguero, Negredo.