Chelsea first took the lead in the first half through Antonio Rüdiger before their first loss of the season was staring them in the face after a brace from Anthony Martial before Barkley struck late to share the points.
These are five things we learnt from the game.
1. Erratic Luiz a liability
If there was any doubt why David Luiz is not rated as a top defender, his mistimed tackle which led to United’s second goal was unambiguous.
Luiz was guilty of committing too much while going for a ball, but he mistimed his tackle on Juan Mata before the Manchester United playmaker passed to Marcus Rashford who assisted Martial to put the Red Devils ahead in the 73rd minute.
2. Barkley proving his worth
An undeniable talent, Barkley broke out at Everton as a youngster destined for greatness. But his promise had begun to fade by the time he joined Chelsea in the summer.
He struggled initially, but in recent weeks, the 24-year-old has shown glimpses of what he promised earlier on in his career and even got rewarded with a recall to the England squad.
He came on in the 69th minute against Manchester United and netted a late equaliser to continue his recent upswing.
3. Morata not the answer for Chelsea
On a day when Manchester United paid a lot of attention on Eden Hazard, Chelsea rarely threatened in attack. This was the day they needed Alvaro Morata the most but the striker showed why he shouldn’t be the one leading the line for Chelsea.
He couldn’t trouble the Manchester United defence in any way and wasn't swift enough to convert his best chance of the game.
It’s a refreshing time at Chelsea so far this season, Maurizio Sarri has come in with a brand of football that is aesthetically pleasing and all their best players including Hazard look happy again.
There is a lot to look forward to, but they need more than Morata to win titles.
4. Jorginho, a blessing and a curse
Since Jorginho followed his boss Sarri from Napoli to Chelsea this summer, he has been the one to translate the basics of Sarriball on the pitch for the manager.
From the base of a three-man midfield, he has been a boon for Chelsea but against top teams, his weakness has been exploited.
Against Manchester United, he failed to track runners inside and around the box, a job primarily for any player in his position.
For United’s second goal, a defensive midfielder in Jorginho’s position would have covered up for Luiz who had mistimed a tackled and harry Rashford who had collected a pass before assisting Martial for the goal.
5. Martial sends his message to Mourinho
The story of the stern relationship between Martial and his Manchester United manager Mourinho has been well told.
For some reasons, Mourinho had Martial out of his starting before he was forced to start the forward after a couple of bad results.
Martial in recent weeks has been proving to be a worthy starter at the club. Against Chelsea at Stamford Bridge, he was at his best again, causing troubles for the opposition defenders and scoring a brace.