Jose Mourinho's side were playing catch-up, quite literally, from the very first minute after Pedro's goal put the Blues ahead, and from then on, it was an uphill struggle against the towering confidence of Antonio Conte's men.
If you're a United supporter, you could be forgiven for thinking that this was rock bottom. There have been plenty of difficult moments since Sir Alex Ferguson put his feet up three years ago, but as bad days at the office go, this was among the very worst.
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As the club reflect on the result this evening, things have now taken a turn for the downright awful.
After such a worrying display by United's defence, Mourinho has now confirmed that Eric Bailly appears to have sustained a serious knee ligament injury.
While the former Villarreal man still needs to undergo a scan, the likelihood is he could be out for several months if it's as bad as first feared - and that's something his team simply can't afford.
"I'm afraid it's a bad injury," Mourinho told the assembled press.
"It's in the ligament area. It's really bad."
Bailly, who has been a hit since arriving this summer, was taken off in the 52nd minute at Stamford Bridge, though it wasn't immediately clear how serious his injury could be.
United fans react
Once the news was out, it's safe to say it did not go down well with United fans, who really didn't need to be kicked while they were already down.
The centre-back is supposed to be heading to the African Cup of Nations with the Ivory Coast in January, so United could do with reinforcements anyway.
And the displays of Chris Smalling and Daley Blind will hardly have put Mourinho at ease, as arguably all of Chelsea's goals could have been prevented.
All in all, United's defence is not looking at all healthy, and this is the last thing they needed as they try and recoup from such a horrendous result.
Can Manchester United cope without Eric Bailly? Have your say in the comments.
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