Not only was this the first meeting of the season between the two Manchester clubs, but it was also the continuing rivalry of two of the game's most successful managers in the modern era.
Now they will pit their wits against each other from the less sunny climes of the North West of England. The weather may not be on a comparison with Spain, but once they make their way home after their first derby experience they will realise that the passion and hatred between the two rival fans are certainly hotter.
Mourinho's first derby starting XI saw some minor changes with the inclusion of Mkhitaryan, who would start his first league game and the return of Lingard after injury: De Gea, Valencia, Blind, Bailly, Shaw, Fellaini, Pogba, Lingard, Mkhitaryan, Rooney and Ibrahimovic.
Once again Mourinho's defence was unchanged, which meant Smalling would have to bide his time a little longer. Fellaini kept his spot alongside Pogba in midfield with Ibrahimovic once again leading the line up front with Rooney slotted in behind him.
So the stage was set for the 172nd instalment of the battle of Manchester.
City got the match underway amid a highly charged atmosphere that was certainly the loudest heard at the Theatre of Dreams in a very long time.
The visitors created the first opening as De Bruyne whipped a low cross across the United box which thankfully evaded everyone. Lingard started out on the left with Mkhitaryan occupying the right channel. Lingard seemed to struggle to begin with after he misplaced passes and was slow to interact with his teammates.
At the back, Bailly was in the same fine form that has won him so many plaudits in his new United career. His gung-ho approach to defending is exactly what United have missed since Vidic departed.
The home side was guilty of giving the ball away too easily and this hit home as City drew the first blood on the quarter hour mark.
Rooney's attempted pass to set Mkhitaryan off and running down the right was blocked and the Armenian gave up the chase for the ball all too easily. The ball was collected down by his own corner flag by Kolarov and after exchanging passes with his keeper he hoofed a long pass forward which was headed on by Iheanacho and there was De Bruyne who managed to nip in ahead of Blind to collect the ball and coolly slotted it into the corner of De Gea's net.
There was an extremely close call for offside against Mkhitaryan as he raced onto a ball through the middle and was upended in the penalty area.
The opening half an hour belonged to the blues as they were the first to every ball and the reds were very careless with their positional play. At least Fellaini was covering the pitch and getting in some sturdy defensive work to help out his back four.
Then, ten minutes before half time disaster for United as City extended their lead. De Bruyne was the thorn in United's side once again as his snapshot rebounded off De Gea's far post into the path of Iheanacho who had the easiest of tasks to slot the ball home as the home defence appealed for offside. It was Blind who had played the attacker onside.
United captain Rooney was guilty of giving the ball away twice while his team were in promising positions. That summed up the way United had played up to that point.
However, it was from a Rooney free-kick that United pulled a precious goal back. The captain floated over a high ball into the area which looked easy for new City keeper Bravo, but he somehow misjudged the ball, flapped and there was new hero Ibrahimovic to smack the ball into the net. The big Swede's technique made it look so easy as he netted his fifth goal in as many games.
That was followed by complete mayhem in the City defence as the keeper inexplicably presented the ball on a plate for Ibrahimovic, but his first time shot was far too weak.The visiting keeper started to show some nerves and dodgy decision making on his debut.
Half time and at least United had started to show some fight towards the end of the half. Some of the players were not having a good time of it and their concentration was not on song as City made them pay for some poor play.
Rashford had an immediate effect on the match as his speed took him down the left and he produced a wonderful cross which Ibrahimovic met but put it over the bar.
The introduction of Rashford completely changed the tempo of United's game as his awareness, speed and overall ability gave the City defenders a lot to ponder.
There were two bookings in quick succession for United as they chased the game. One each for Ibrahimovic and Fellaini. The Belgium was adjudged to have used his elbow, not for the first time in his career.
It was all United now as the fans urged their heroes to attack and attack they did this time down the right when a cross was averted by the elbow of Otamendi. For the third time in the game referee Clattenburg waved away the home side's claims for a spot kick.
There was a distinctive difference to United's play as they had an urgency about them that had been lacking in the first half.
The pace of Rashford almost paid off as he raced towards the penalty area and struck a well-aimed shot into the net only for it to be rightly called for offside against Ibrahimovic. So unlucky for both the youngster and his side who deserved to be back on level terms.
United keeper De Gea produced the goods to keep his side in the game from a spate of City corners with a double save followed by a catch at full stretch to prevent a certain goal.
At the other end, United were also guilty of wasted opportunities when on the attack and needed to aim more balls at the hapless keeper who looked like a fish out of water.
The last change of the match for United saw Martial enter the fray in place of Shaw to add an extra body to the attack for the remaining ten minutes.
Rooney was cautioned for catching the keeper late after Bravo had dithered on the ball in his own area. As a referee, Clattenburg gave the home side nothing in the way of balanced decisions and the Rooney caution was another example of this.
In the next attack, Rooney stayed on his feet after being caught inside the area. He probably realised that if he had gone to ground the referee wouldn't have given anything anyway.
In the end, it was a disappointing first defeat of the season for Mourinho's men, but in fairness they didn't start to play until the introduction of Rashford at the beginning of the second half. In hindsight, maybe he should have started from the off.
United's cause wasn't helped by a terrible performance by referee Clattenburg who made a number of poor decisions. The main one being the Bravo challenge on Rooney. The inconsistency of Premier League referees is a huge problem that has to be looked into as each game throws up more than one contentious decision week in week out.
It has to be said Mourinho got it wrong in his team selection with the choice of Lingard, who had only just come back from injury and Mkhitaryan who had picked up a knock while on international duty and was clearly not in the right mindset.
Obviously, Mourinho's tactics are still a work in progress and one poor result doesn't spell a disaster. However, some of the players need to raise their game to justify their inclusion.
A bad day at the office and one in which lessons will hopefully be learnt by Mourinho and his coaches as they try to pick up the players ahead of their opening Europa League game against Feyenoord.
Until then thanks for reading.