Make no mistake, this is a body blow to Manchester United.
Home defeats early in both domestic cup competitions means they now require an unlikely Champions League triumph to avoid going without a trophy for a fifth straight season.
Rumours persist that United's players are unsure of what is being asked of them by Rangnick, and the fact two players - Anthony Martial and Jesse Lingard - have gone to the media to contradict his comments is startling. Certainly, it is difficult to imagine any player doing that in Sir Alex Ferguson's time.
United have little time to lick their wounds.
Over an eight-day period, they face Burnley, Southampton and Brighton, a series of games leading up to their return to the Champions League during which they should really consolidate their top-four place in the Premier League.
Anything less than nine points, though, and the alarm bells will start getting louder and louder.
'I thought it would get chalked out'
Inevitably, that Middlesbrough goal was a big talking point after the game.
"How can it be accidental if he controls the ball up in the air with his hand?" Manchester United interim boss Ralf Rangnick queried after the game. "It was clear it should not stand but in the end I was really surprised it stood."
Even Boro boss Chris Wilder fully expected to see it ruled out: "I thought straight away it was handball. I thought it would be chalked out and delighted it wasn't."
Wilder added: "You cannot get any better than winning at Old Trafford on a Friday night.
"We are delighted, the opposition will be wondering how they did not progress, it is the magic of the cup, we rode our luck, took our chances and took it to a shootout.
"You can't do anything when it goes to penalties, you just hope they are positive and they took a fabulous approach. You give yourself an opportunity to witness scenes like tonight, 10,000 fans coming down the road and going away happy."
Watch the action
Here are the highlights, along with a clip of that Boro equaliser, so you can make up your own mind on whether it should have stood...
Video content
Video caption: FA Cup: Manchester United 1-1 Middlesbrough - Middlesbrough win 8-7 on penaltiesFA Cup: Manchester United 1-1 Middlesbrough - Middlesbrough win 8-7 on penalties
Video content
Video caption: 'It definitely hit his hand!' Middlesbrough score controversial equaliser'It definitely hit his hand!' Middlesbrough score controversial equaliser
Middlesbrough joy as Man Utd crash out
Getty ImagesCopyright: Getty Images
So then, let's have a little look back at last night's events at Old Trafford.
In case you've missed it completely, Manchester United crashed out of the FA Cup as Championship side Middlesbrough came from behind and then emerged victorious in a nail-biting 16-shot penalty shootout.
Young striker Anthony Elanga ballooned his shot over the bar to give Chris Wilder's side a win that was celebrated in enthusiastic fashion by a 9,000-strong visiting support.
Middlesbrough's equaliser was a controversial one, scored by Matt Crooks, who tapped home despite Duncan Watmore clearly handling in the build-up.
However, they only had themselves to blame after failing to take numerous chances in a game where they had 30 shots at goal, the clearest of which came when Cristiano Ronaldo missed a penalty in the first half.
Kenedy, Kenedy, Kenedy, sa-wing batter!
Chelsea v Plymouth (12:30 GMT)
Chelsea boss Thomas Tuchel says Brazilian wing-back Kenedy has a huge opportunity to find his feet at Stamford Bridge after returning from his fifth loan spell away from the club.
The 25-year-old has been at Chelsea since 2015 but has failed to cement his place with the Blues under five different managers.
With first choice full-backs Reece James and Ben Chilwell out with long-term injuries, Tuchel says he is happy to give Kenedy the chance to stake a claim for a starting position.
“He’s very talented and this is a huge opportunity for him,” he said. “He got a second chance here and he wants to take it.
“His duty now is to get fit and then we need to give him some minutes, whatever that looks like. It’s about having the right mentality and mindset to take the opportunities when they come.
“He will fight for a place and I expect others to take on that fight too to stop him from taking their place in the team.”
Chelsea's game with Plymouth in the FA Cup fourth round is live on the BBC Sport website and app, on the Red Button and BBC iPlayer on Saturday, 5 February (12:30 GMT).
Team news - Blues name strong team
Chelsea v Plymouth (12:30 GMT)
Chelsea make just one change to the side that beat Tottenham in the Premier League nearly a fortnight ago.
Andreas Christensen replaces Thiago Silva, who has been on international duty with Brazil. Kenedy, who has not played for the Blues in nearly four years, is among the substitutes.
Plymouth make three changes to the team that beat Doncaster 3-1 away from home in League 1 last weekend.
Panutche Camara, Danny Mayor and Jordon Garrick come in, replacing Ryan Broom, Adam Randell and Niall Ennis.
This
is West Ham’s first fixture since January 22 when the Hammers were narrowly
beaten by Manchester United.
David
Moyes makes eight changes to his side, with only Alphonse Areola, Kurt Zouma and Jarrod Bowen keeping their places in the starting XI.
Club captain Mark Noble starts his first match since December 28.
West Ham XI:
Areola, Fredericks, Zouma, Diop, Johnson, Noble, Kral, Vlasic, Benrahma, Bowen, Yarmolenko.
Twitter/West HamCopyright: Twitter/West Ham
Post update
We're getting team news through from the two 12:30 GMT kick-offs in the FA Cup. It is fair to say that Chelsea aren't taking any chances. West Ham have made a few changes, though...
No replays, midweek games next round, five subs
There have been a few tweaks to the usual way of things for the FA Cup in 2021-22...
Fourth-round replays have been scrapped this season to help with the fixture backlog caused by Covid postponements.
Ties will be played to a finish on the day, with 30 minutes of extra time and penalties to decide the winners if required.
Today, teams are playing for a place in the fifth round which will take place across the first midweek in March.
Clubs can name nine substitutes and use five.
Tuchel tests positive for Covid-19
Chelsea v Plymouth (12:30 GMT)
Chelsea have confirmed that manager Thomas Tuchel has tested positive for Covid-19.
The German will now follow self-isolation protocols and expects to join his players in Abu Dhabi for the Club World Cup next week.
The Chelsea squad are due to fly out to the United Arab Emirates after today's game against Plymouth.
Video caption: FA Cup: Shocks, slips and celebrations - FA Cup Third Round magicFA Cup: Shocks, slips and celebrations - FA Cup Third Round magic
There are numerous ways you can follow all that fun here at the BBC.
To start with, we'll have live text coverage (just like this) of games from all three competitions.
BBC One is showing the tie between Kidderminster and West Ham (12:30) - a repeat of the fifth-round tie 28 years ago when the Hammers won 1-0 at Aggborough.
Plymouth's first visit to Chelsea since 1988 is also on Saturday at 12:30 on the BBC iPlayer, BBC Sport website, app and Red Button.
Later on Saturday the tie between Cambridge and Luton Town (17:30) is also available to watch on the BBC iPlayer, BBC Sport website, app and Red Button.
BBC Radio 5 Live has three live commentaries on Saturday - Kidderminster-West Ham (12:30), Crystal Palace v Hartlepool (15:00) and Tottenham v Brighton (20:00). Former West Ham and England keeper Rob Green will be in the commentary box at Kidderminster alongside John Murray.
They'll also have updates from around the grounds.
Premier League muscling in
Burnley v Watford (18:00 GMT)
Premier League
Oh, hang on... there's also a Premier League game today!
It's a big one too, between the division's two bottom sides - Watford and Burnley. A six-pointer if ever there was one.
We'll have live text coverage of that too. Kick-off is at 18:00 GMT.
You won't know where to focus your attention.
WSL and Afcon action
At the same time as those two early FA Cup ties, there is also some WSL action, with Arsenal hosting Manchester United.
And then later, at 19:00, there is the third/fourth-place play-off in the Africa Cup of Nations, with hosts Cameroon facing Burkina Faso.
FA Cup ties
Let's start with those 12 Cup fixtures, which look like this...
12:30 GMT: Chelsea v Plymouth, Kidderminster v West Ham
15:00: Crystal Palace v Hartlepool, Everton v Brentford, Huddersfield v Barnsley, Man City v Fulham, Peterborough v QPR, Southampton v Coventry, Stoke v Wigan, Wolves v Norwich
17:30: Cambridge v Luton
20:00: Tottenham v Brighton
That's not all, though...
Post update
The FA Cup fourth round got off to a dramatic, gripping start last night (and a wonderful one if you're a Boro fan, and indeed for many other supporters of anyone but Manchester United).
One tie down, one shock in the bag.
Today, there's the potential for a few more, starting at 12:30 GMT with what could be the biggest of the round as West Ham travel to non-league Kidderminster Harriers.
We have 12 FA Cup ties in total today, and much, much more.
Live Reporting
Gary Rose and Neil Johnston
All times stated are UK
What next for Manchester United?
Simon Stone
BBC Sport at Old Trafford
Make no mistake, this is a body blow to Manchester United.
Home defeats early in both domestic cup competitions means they now require an unlikely Champions League triumph to avoid going without a trophy for a fifth straight season.
Rumours persist that United's players are unsure of what is being asked of them by Rangnick, and the fact two players - Anthony Martial and Jesse Lingard - have gone to the media to contradict his comments is startling. Certainly, it is difficult to imagine any player doing that in Sir Alex Ferguson's time.
United have little time to lick their wounds.
Over an eight-day period, they face Burnley, Southampton and Brighton, a series of games leading up to their return to the Champions League during which they should really consolidate their top-four place in the Premier League.
Anything less than nine points, though, and the alarm bells will start getting louder and louder.
'I thought it would get chalked out'
Inevitably, that Middlesbrough goal was a big talking point after the game.
"How can it be accidental if he controls the ball up in the air with his hand?" Manchester United interim boss Ralf Rangnick queried after the game. "It was clear it should not stand but in the end I was really surprised it stood."
Even Boro boss Chris Wilder fully expected to see it ruled out: "I thought straight away it was handball. I thought it would be chalked out and delighted it wasn't."
Wilder added: "You cannot get any better than winning at Old Trafford on a Friday night.
"We are delighted, the opposition will be wondering how they did not progress, it is the magic of the cup, we rode our luck, took our chances and took it to a shootout.
"You can't do anything when it goes to penalties, you just hope they are positive and they took a fabulous approach. You give yourself an opportunity to witness scenes like tonight, 10,000 fans coming down the road and going away happy."
Watch the action
Here are the highlights, along with a clip of that Boro equaliser, so you can make up your own mind on whether it should have stood...
Video content
Video content
Middlesbrough joy as Man Utd crash out
So then, let's have a little look back at last night's events at Old Trafford.
In case you've missed it completely, Manchester United crashed out of the FA Cup as Championship side Middlesbrough came from behind and then emerged victorious in a nail-biting 16-shot penalty shootout.
Young striker Anthony Elanga ballooned his shot over the bar to give Chris Wilder's side a win that was celebrated in enthusiastic fashion by a 9,000-strong visiting support.
Middlesbrough's equaliser was a controversial one, scored by Matt Crooks, who tapped home despite Duncan Watmore clearly handling in the build-up.
However, they only had themselves to blame after failing to take numerous chances in a game where they had 30 shots at goal, the clearest of which came when Cristiano Ronaldo missed a penalty in the first half.
Kenedy, Kenedy, Kenedy, sa-wing batter!
Chelsea v Plymouth (12:30 GMT)
Chelsea boss Thomas Tuchel says Brazilian wing-back Kenedy has a huge opportunity to find his feet at Stamford Bridge after returning from his fifth loan spell away from the club.
The 25-year-old has been at Chelsea since 2015 but has failed to cement his place with the Blues under five different managers.
With first choice full-backs Reece James and Ben Chilwell out with long-term injuries, Tuchel says he is happy to give Kenedy the chance to stake a claim for a starting position.
“He’s very talented and this is a huge opportunity for him,” he said. “He got a second chance here and he wants to take it.
“His duty now is to get fit and then we need to give him some minutes, whatever that looks like. It’s about having the right mentality and mindset to take the opportunities when they come.
“He will fight for a place and I expect others to take on that fight too to stop him from taking their place in the team.”
Chelsea's game with Plymouth in the FA Cup fourth round is live on the BBC Sport website and app, on the Red Button and BBC iPlayer on Saturday, 5 February (12:30 GMT).
Team news - Blues name strong team
Chelsea v Plymouth (12:30 GMT)
Chelsea make just one change to the side that beat Tottenham in the Premier League nearly a fortnight ago.
Andreas Christensen replaces Thiago Silva, who has been on international duty with Brazil. Kenedy, who has not played for the Blues in nearly four years, is among the substitutes.
Chelsea XI: Arrizabalaga, Azpilicueta, Rudiger, Christensen, Sarr, Mount, Jorginho, Kovacic, Ziyech, Lukaku, Hudson-Odoi
Plymouth make three changes to the team that beat Doncaster 3-1 away from home in League 1 last weekend. Panutche Camara, Danny Mayor and Jordon Garrick come in, replacing Ryan Broom, Adam Randell and Niall Ennis.
Plymouth XI: Cooper, Edwards, Wilson, Scarr, Gillesphey, Grant, Camara, Houghton, Mayor, Jephcott, Garrick
Team News - Noble starts
Kidderminster v West Ham (12:30 GMT)
Kidderminster boss Russell Penn has made three changes to the side that beat Leamington 3-0 in the National League North last time out.
Mark Carrington, Ashley Hemmings and Geraldo Bajrami replace Lewis Montrose, Jaiden white and Devonte Redmond.
What an occasion for those 11 starters!
Kidderminster Harriers: Simpson, Penny, Richards, Cameron, Austin, Carrington, Morgan-Smith, Hemmings, Sterling, Bajrami, Preston.
This is West Ham’s first fixture since January 22 when the Hammers were narrowly beaten by Manchester United.
David Moyes makes eight changes to his side, with only Alphonse Areola, Kurt Zouma and Jarrod Bowen keeping their places in the starting XI.
Club captain Mark Noble starts his first match since December 28.
West Ham XI: Areola, Fredericks, Zouma, Diop, Johnson, Noble, Kral, Vlasic, Benrahma, Bowen, Yarmolenko.
Post update
We're getting team news through from the two 12:30 GMT kick-offs in the FA Cup. It is fair to say that Chelsea aren't taking any chances. West Ham have made a few changes, though...
No replays, midweek games next round, five subs
There have been a few tweaks to the usual way of things for the FA Cup in 2021-22...
Fourth-round replays have been scrapped this season to help with the fixture backlog caused by Covid postponements.
Ties will be played to a finish on the day, with 30 minutes of extra time and penalties to decide the winners if required.
Today, teams are playing for a place in the fifth round which will take place across the first midweek in March.
Clubs can name nine substitutes and use five.
Tuchel tests positive for Covid-19
Chelsea v Plymouth (12:30 GMT)
Chelsea have confirmed that manager Thomas Tuchel has tested positive for Covid-19.
The German will now follow self-isolation protocols and expects to join his players in Abu Dhabi for the Club World Cup next week.
The Chelsea squad are due to fly out to the United Arab Emirates after today's game against Plymouth.
BBC coverage
BBC One
Video content
There are numerous ways you can follow all that fun here at the BBC.
To start with, we'll have live text coverage (just like this) of games from all three competitions.
BBC One is showing the tie between Kidderminster and West Ham (12:30) - a repeat of the fifth-round tie 28 years ago when the Hammers won 1-0 at Aggborough.
Plymouth's first visit to Chelsea since 1988 is also on Saturday at 12:30 on the BBC iPlayer, BBC Sport website, app and Red Button.
Later on Saturday the tie between Cambridge and Luton Town (17:30) is also available to watch on the BBC iPlayer, BBC Sport website, app and Red Button.
BBC Radio 5 Live has three live commentaries on Saturday - Kidderminster-West Ham (12:30), Crystal Palace v Hartlepool (15:00) and Tottenham v Brighton (20:00). Former West Ham and England keeper Rob Green will be in the commentary box at Kidderminster alongside John Murray.
They'll also have updates from around the grounds.
Premier League muscling in
Burnley v Watford (18:00 GMT)
Premier League
Oh, hang on... there's also a Premier League game today!
It's a big one too, between the division's two bottom sides - Watford and Burnley. A six-pointer if ever there was one.
We'll have live text coverage of that too. Kick-off is at 18:00 GMT.
You won't know where to focus your attention.
WSL and Afcon action
At the same time as those two early FA Cup ties, there is also some WSL action, with Arsenal hosting Manchester United.
And then later, at 19:00, there is the third/fourth-place play-off in the Africa Cup of Nations, with hosts Cameroon facing Burkina Faso.
FA Cup ties
Let's start with those 12 Cup fixtures, which look like this...
12:30 GMT: Chelsea v Plymouth, Kidderminster v West Ham
15:00: Crystal Palace v Hartlepool, Everton v Brentford, Huddersfield v Barnsley, Man City v Fulham, Peterborough v QPR, Southampton v Coventry, Stoke v Wigan, Wolves v Norwich
17:30: Cambridge v Luton
20:00: Tottenham v Brighton
That's not all, though...
Post update
The FA Cup fourth round got off to a dramatic, gripping start last night (and a wonderful one if you're a Boro fan, and indeed for many other supporters of anyone but Manchester United).
One tie down, one shock in the bag.
Today, there's the potential for a few more, starting at 12:30 GMT with what could be the biggest of the round as West Ham travel to non-league Kidderminster Harriers.
We have 12 FA Cup ties in total today, and much, much more.
Up for the Cup
Who says the FA Cup has lost its magic?