What followed was a fiercely competitive contest between the two teams which was captivating for the committed fan and the neutral alike.
Sadly, it finished with the ugly side of football partisanship rearing its ugly head again.
You would have thought that the general sense of shock following the Hillsborough papers would leave fans mindful of their collective responsibility to each other. Fencing was removed from grounds after that tragedy, which had originally been put in place to protect supporters and players from pitch invasions and missiles.
The Europeans still hark back to the "English disease" (which got clubs banned from Europe after Heysel) despite crowds in countries such as Italy, Holland and Germany being worse behaved. Where, for example, in the UK can you get away with taking flares into grounds, let alone igniting them?
There will always be a hard core element, however, who burn with uncontrollable rage, who seek attention or are basically nasty, especially those who are pervaded by racism.
We saw all of that in the ugly scenes at the end of the match that could have seen Rio Ferdinand blinded in one eye or otherwise physically assaulted. Despite Wayne Rooney drawing the referee's attention to his bombardment by coins earlier, the referee decided to do nothing.
We await the outcome of the FA and Manchester City/GMP investigations, but Sir Alex struck a serious note in remarking that nothing had been done about a worse bombardment at Stamford Bridge.
Surely one of the matches of the season?
The match itself was a comment on the current state of the rivalry.
In the past there has been the impression that neither side wanted to lose. This was clearly the case at the end of last season, when City edged it 1-0.
This time, Sir Alex had set his stall out very clearly, with a formation and a way of playing that should bring 4-4-2 back into fashion at Old Trafford.
Both sides seemed to set up as a 4-2-3-1, but for much of the game United were able to play a high 4-4-2 thanks to the industry of particularly Cleverley and Rooney, until Sir Alex settled for 4-5-1 at the end.
This was a blood and thunder affair which was made to seem more ugly than it was thanks to the modern habit of falling over for the slightest touch.
Martin Atkinson refereed it well, except for stopping play when Yaya Toure was away, a clear penalty claim against Kolo Toure on Patrice Evra and his over-zealous assistant who wrongly disallowed an Ashley Young goal that would surely have finished the match as a contest.
We shan't get too carried away with gratitude for that error, which led to the match being a nail-biter to the end.
Those decisions did leave Roberto Mancini seeming somewhat unconvincing in describing Manchester United as "lucky". He did not seem to have noticed that United's finishing was more clinical and their defence more frugal.
He was at least honest enough to condemn his own players for individual culpability. One was Balotelli, who continues to be an enigma.
So the first difference between the two teams was the tactical set-up, where Mancini took a tragic gamble in playing Balotelli, hoping the Euro 2012 star would turn up. He didn't—in fact he didn't turn up at all.
So United gradually gained the ascendancy and it was their own occasionally wayward star Wayne Rooney who was the hero on the day with a "Man of the Match" performance.
In defence of Manchester United
With their worst defensive start to the Premier League for years, the United players are always going to get "pelters" for conceding any goals. Gone, it seems, are the days of a string of 1-0 wins. And thank goodness for that.
There can be little doubt that United are the most entertaining team to watch right now. Apart from the fact that they have had to come back from conceding the first goal 15 times already, they are box office if you want end-to-end action.
By half time against Reading for example, they could have been 6-3 up and supporters weren't mad in dreaming of 10-3 before they shut up shop.
Against City the whole side was much better organised. If there was one minor criticism it was that nobody was standing on the edge of the box at all, let alone after the first goal which Toure scored from that position.
United seemed to have forgotten that Balotelli opened the six-goal floodgates from exactly the same position at Old Trafford last season.
But to criticise this aberration is to seek perfection, because United defended the set-pieces well, with De Gea looking like a new man as he rushed confidently off his line. The second goal was down to an unfortunate clearing header by Van Persie that fell to Zabaleta, who managed to steer it through the luckless Phil Jones's legs.
City, on the other hand, showed some of the defensive frailty that had seen them eliminated from the Champions League as the first English team to win no Group stage matches.
Whether it's tinkering about with three at the back, or the reliance on zonal marking, Mancini still has problems to sort out. Sir Alex had clearly taken some pointers from how Dortmund had tormented City in their own half at the Etihad, and United were a revelation in their pressing and hounding.
So United's case for attack and defence was just made on points.
Is the title destined for Manchester?
Despite Fernando Torres' apparent rebirth under Benitez, surely one of these teams will take the title again. It's not just their quality in depth; it's the passion and commitment.
United's is beyond question and was there in spades on Sunday, both in the crowd and every player on the pitch. Several players had their best game of the season.
City were equally far less lacklustre and more committed than they had been in the UCL—not surprising, really as they have more to gain from Manchester derbies than United.
While City now sit six points behind their cross-City rivals, both sides played as if this was a title decider. It is not, although it may well be cited if United go on to claim the trophy.
City will recover from this, but they have immediate serious concerns in losing two of their most influential players.
Kompany seemed to be carrying an injury for the last two weeks. Yaya Toure got a knock from barging into the innocent Tom Cleverley (who refused to be intimidated by the man mountain in blue).
Geoffrey Boycott once likened batting against Jeff Thomson as being as daft as standing on a motorway in front of the traffic. Playing against Toure in midfield must feel pretty similar. Like Jonah Lomu for the All Blacks, you can take him on, but he'll run straight through you.
This time he hardly ran through the admirable Cleverley and Carrick.
So the match probably summed up the state of play in the Premier League rivalry.
United deservedly edged it and may go on to win the title. They were better organised and more clinical at both ends of the pitch. City had the lion's share of possession, but United, like Dortmund, had the territorial advantage with their high counter-attacking game.
With Vidic about to return, key players back from injury and other players emerging (like Powell, Buttner and Anderson, at last), United are coming onto their form at exactly the right time.
Normally stronger after Christmas, they have a run of games up till then that should see them with a comfortable lead going into the New Year.
City have the Africa Cup to contend with and many more injuries than in their extraordinary year last season.
Will the Champions League exit be a factor?
Now this is an interesting point. City won't even have "Thursday nights on the box" to contend with. Unless they get a good run in the FA Cup, their players will be more rested than United's.
But United have a deeper squad. There is also the matter of momentum. Carlos Tevez joined City because he wanted to win the Champions' League and such. They have never looked remotely like progressing. Imagine his chagrin as City lost on Saturday to the club he left by choice.
So City will be fresher, but Sunday's match suggested there is still an overhang of disappointment and deflation. When you join City for big money and the prospect of dominating Europe, what happens when you blow out of the Champions' League with the worst performance ever and don't even qualify for the Europa League?
Even Celtic qualified for the knockout stage in a Group dominated by Barcelona, whom they beat!
So it must be a factor for the players, and especially for Mancini. The manager is looking increasingly under pressure. The project was due to deliver Champions' League qualification and surely progress by now; otherwise why spend nearly £500 million?
So yes, United have the Champions' League to think about, but to put it in perspective, it is a maximum of seven additional games.with all the euphoria that goes with achievement. Realistically United may only have to play a maximum of four of those.
Set that against the African Cup of Nations, which is also in the New Year, and they pretty much balance each other out.
But it may well depend on signings in January. Everyone is agreed that United need an additional midfielder at the very least. Scholes and Giggs are literally on their last legs.
United need to ship out Nani and City Balotelli, but can they get the like for similar replacements they desire? January is not a good time for choice, especially where players are Champions' League cup-tied.
Their respective needs
Based on Sunday, both squads look tired and in need of refreshment.
United have Fletcher afflicted by a life-changing medical condition. Carrick, Ferdinand, Evra and especially Scholes and Giggs aren't getting any younger. Anderson and Cleverley appear to be injury prone; Nani has lost the plot.
City need to get rid of the liability Balotelli has become and ship in a striker comparable to Van Persie, if the purse strings allow. They also need freshening up in defence and midfield. And God knows what would happen if Joe Hart was long term injured?
Of the two, United look like they could muddle through indefinitely with someone like Kevin Strootman and a replacement similar to Nani.
City are looking like their purchasing is now suspect. Balotelli is a joke; Nasri lost the plot on Sunday; Lescott and Kolo Toure seem to be yesterday's men; Milner and Barry may be past their best and there seems to be little trust in the Academy product.
Maybe overall this is a comment on the Premier League in general; two years ago it was regarded as the strongest league in the world. Now only two clubs have qualified for the knockout stages of the UCL and teams like Atletico Madrid, Juventus and Dortmund can beat us at will.
That doesn't change the fact that Manchester is likely to dominate the Premier League agenda for years to come.
Sunday's match showed that the newly revived rivalry is richly alive, from the pitch to the terraces. The bragging rights are worth fighting for. United may be once more in the ascendancy but, FFP permitting, the "new kids on the block" won't lie down.
But if the current generation at City loses heart, one thing will never change. United will still be one of the biggest clubs on the planet and they will go on winning regardless. It's in their DNA, and it's what ultimately made the difference on Sunday.