Goals from David Silva and Nicólas Otamendi either side of a Marcus Rashford strike were enough for City, the better side on the day, to increase their lead at the top of the league to 11 points over United in second.
The irony in Mourinho's set-up
United set out to stifle their crosstown rivals, who have still yet to lose a game in the league this season. The most disappointing and frustrating part of the loss for United is that they did manage to keep City’s rampant attack under wraps for large spells of the game. Although goalscorer Silva and Kevin De Bruyne had large spells of possession, they found it difficult to create concrete scoring chances from the run of play.
The two City goals came from horrendous defending mistakes by United. Near the end of the first half, the Reds fell fast asleep at a corner. The ball caromed off Romelu Lukaku and towards the goalmouth, where Silva, who Jesse Lingard had stopped tracking, had a simple finish to make it 1-0.
Nearly ten minutes after the restart, Lukaku found himself the culprit of a worse defensive giveaway. Silva whipped in a free kick from the left wing that looked as though it was headed over everyone. Lukaku looked to clear, slammed his clearance off Chris Smalling, and into the path of Otamendi who too had a tap-in.
José Mourinho’s playing style in big games is predicated on minimising mistakes. He subscribes to a theory that says that in a big game, with all of the pressure that entails, the team with the ball is more likely to make a costly mistake.
Thus, he cedes possession, attempting to minimise the risk factor, and force his opponent’s hand. On Sunday, his side did cede possession, and a bad error from Fabian Delph handed Rashford the equaliser.
Yet, the irony was that in the end, United made the worse errors, and it cost them the game. It could well cost them the title too.
City have it all in their hands
With the victory, City have won 14 matches in a row, a record in the Premier League for consecutive wins in a single season.
Their record-setting pace to the season has seen them play the best football in Europe – although Paris Saint-Germain might disagree – with their only loss coming in a dead-rubber Champions League tie at Shakhtar Donetsk.
They have 46 points from 16 league matches, with their only draw coming against Everton in the season's opening weeks. While expecting them to keep winning at this pace for the rest of the season is unfair and unrealistic, they also don’t look like anyone will catch them the rest of the way.
United sit in second, 11 points back. This match, the season's most important six-pointer at the top of the table, had handed United a chance to start pulling City back in. Instead, they were well beaten.
While City's two goals did come via defensive mistakes, United did not offer enough going forward to deserve anything from this game.
Mourinho's big-game methodology has produced no shortage of fine and famous results, but it leaves no room for error. United’s errors were punished, and they deserved to lose this game.
Psychological boost crucial
The win provides not just a boost in the table to City, but a psychological one as well. They have shown time and again this season that they are the Premier League's best. They showed it again on Sunday by beating their famous rivals on their own patch.
City's play as of late has not been quite as otherworldly as it was earlier in the season, and they have required late goals to beat some of the league's lesser lights. Yet, nothing will provide a boost to their mental state or to their attacking play quite like beating United at Old Trafford.
Just as this game is worth more in the standings for both teams, so it is for the psychology of both. United knew just how much it mattered, and the result will have the opposite effect on their mentality as it did on City's.
The prospect of catching a team who have only dropped two points from 16 games looks impossible. While City are still alive in the Carabao Cup and will have knockout matches in the Champions League and FA Cup to think about in the new year, so do United. Any notions of a hectic fixture schedule prompting City to drop points are equally true for the Reds.
In the next few weeks, City face several match-ups with teams in a relegation battle, and only play one other top-six team in the next month.
While United's set of fixtures in the near-term looks even softer than City's does, with the way the league leaders are playing, it doesn't feel as though it will make a difference.