The Red side of Manchester was beaten by Chelsea 1-0 as the 20-time Premier League champions continue their dreadful run at Stamford Bridge having only recorded 1 win in their last 15 games at the Bridge.
Alvaro Morata bagged a goal to put the London club ahead after the Manchester United defence finally collapsed after holding the blues at bay for 55 minutes. Let's take a look at what went wrong for the Red Devils:
#5. The positioning of the wingbacks
Jose Mourinho is known for his tactical awareness and expertise but on Sunday against Chelsea, there was a huge flaw in the way he set his team up.
While it has been common for Man Utd to push their fullbacks further up the pitch to provide support on the attack, they had to make amends to their system to defend against the aerial threat of Alvaro Morata, who is constantly looking to get on the end of the many crosses that come his way.
Antonio Conte's side took full advantage of the space left behind by the two former wingers who are now playing as fullbacks for Manchester United.
Valencia and Young were constantly caught out further up at the pitch as United lost possession and Chelsea's master midfield sprayed balls out to Alonso and Zappacosta who often found space on the flanks and were able to get their crosses in.
Eventually, Chelsea were able to take advantage of all this control in the wide areas, and one of their 19 crosses was headed home by Alvaro Morata
#4. Failure to nullify the threat that is Alvaro Morata
Even though the Spaniard failed to score in any of his last six appearances, Alvaro Morata was an obvious threat against United.
Morata was allowed to have as many as 23 touches in the final third including 10 inside the United box. Even though the Spaniard only managed to get 3 shots away, he was a constant threat to the United defence.
The previous point also didn't help Man Utd's cause. With the wingers pushed so far up, the back three of Bailly, Smalling and Jones was really stretched and often left gaps in the middle for Chelsea to exploit with through balls and the excellent dribbling capabilities of both Morata and Hazard.
Because of this stretching of the back three, United's midfield found themselves dug up inside their own half, which allowed space for Azpillicueta to pick an inch-perfect cross for Alvaro Morata not for the first time this season.
#3. Failure to involve Romelu Lukaku and Marcus Rashford
A constant criticism of Romelu Lukaku is that he disappears in big games, and the Chelsea game was no different. While performances like these have earned him a reputation of a "Flat-Track Bully", you have to sympathise with the Belgian and United frontman, who was left stranded alongside Marcus Rashford by his team's midfield.
Manchester United's top scorer had no say in the game whatsoever, and fingers have to be pointed at the Man Utd midfield who have failed to transition from defence to attack smoothly in Paul Pogba's absence.
Lukaku has now failed to score in his last six appearances for the club, his biggest drought in a Man Utd shirt, and the absence of his partner in crime, Paul Pogba is at the heart of this disheartening form for one of Premier League's most ruthless goalscorers.
Marcus Rashford was comparatively involved a lot more, but still not anywhere near enough. When Man Utd started attacking with 20-or so minutes to play, Rashford was constantly dropping deep and drifting wide to support United's last-ditch efforts but the Chelsea defence dealt with him well and kept him pinned on the left flank.
#2. Inviting waves of Chelsea attack
While it is hard to determine whether this was a case of Mourinho's tactics or Antonio Conte tactically outsmarting Manchester United and pinning them into their own half, Chelsea were rampant after they walked out of the dressing room after halftime.
Manchester United absorbed wave after wave of Chelsea attack and felt maybe they could pull off a defensive feat like at Anfield but Azpillecueta had other ideas. He tore open the best defence in the league with a tremendous cross finding fellow Spaniard Alvaro Morata who pulled the Blues into the lead.
United enjoyed possession quite a bit in the early and in the latter stages of the game but were pinned down in their own half for all the time in between. N'Golo Kante's return proved vital for Chelsea as he, Fabregas and Bakayoko completely nullified Man Utd's midfield and left their strikers hungry.
From there, it was just an exercise in patience for Mourinho's men who thought they could absorb all the pressure Chelsea threw at them but a loss of concentration for a breath of a second saw Morata sneak past the United defenders to head home.
#1. Losing possession in key areas
Although Jose Mourinho's team does not play a possession-based game like his predecessor and focuses mainly on hitting teams on the counter, keeping the ball against a side like Chelsea is essential.
No team can afford to let the likes of Hazard, Morata and the magnificent midfield that Chelsea have, dominate the ball, even if that team may have arguably the best defence in the league.
Mourinho's men were very wasteful and impatient in possession and gave the ball away 19 times in the final third and once even in their own box. United tried to play a whopping 79 long balls in an attempt to escape from the hole Chelsea dug them in.
A major yet latent factor in United's inability to keep possession was the return of Chelsea's backroom hero, N'Golo Kanté. As usual, Kanté was all over the pitch covering every blade of grass and eliminating passing options for the United man on the ball.
United failed to counter the 2-time Premier League winner and had to surrender possession and put their backs to the wall in order to absorb all the Chelsea pressure.