Chelsea manager Jose Mourinho said he was "ashamed" and "embarrassed" by his side's fourth-round exit to League One Bradford City on a day of thrilling FA Cup shocks.
"It's a disgrace for a big team to lose to a small team from a lower league," said Mourinho, 51.
"Me and the players must feel ashamed."
An incredible round of shocks began on Friday night when League Two Cambridge United held Manchester United to a goalless draw and continued on Saturday lunchtime as Swansea City exited at the hands of Championship Blackburn Rovers.
The two served as little warning as Premier League leaders Chelsea followed suit, while second-placed City and third-placed Southampton also saw hopes of a Wembley trip ended.
The Saints were beaten 3-2 at St Mary's by Crystal Palace while eight-time winners Tottenham missed out on a place in Monday's fifth-round draw as they conceded twice in the closing seven minutes to lose at home to Leicester City., and Liverpool drew with Bolton.
But no side spanned a gulf in class quite like Bradford City, who became the first team to ever put four goals past a Mourinho side in a home game despite being 49 places below Chelsea in England's football pyramid.
The former Real Madrid, Inter Milan and Porto boss entered the Bantams' dressing room after the game, congratulating players individually.
"I repeat a word I used before this match - It's a disgrace for a big team to lose to a small team from a lower team," said Mourinho, who won the FA Cup during his first spell at Chelsea in 2007.
"Frustration is not the right word, embarrassed would be more appropriate."
Bradford upset Premier League opponents en route to a League Cup final appearance in 2013 and became the first third-tier team to score four against the Blues in 57 years.
Manager Phil Parkinson told BBC Radio 5 live: "The lads are absolutely bouncing in that dressing room and what they've done today will be remembered for a very long time - not just in Bradford but all around the country.
"Playing the league leaders and one of the best teams in Europe and scoring four goals... That's going to take some beating."
'Worst squad we've ever seen'
A jubilant Bradford City co-chairman Mark Lawn told BBC Radio 5 live Parkinson inherited the "worst squad we have ever seen" when appointed in 2011 and that this fixture allowed the club to break even from a £1m overspend this season.
"We've just beaten a team that is as good as Barcelona," said Lawn. "It just goes to show Match of the Day should have us on telly all the time, because we score you goals."
Manchester City manager Manuel Pellegrini refuted any suggestion his side's recent trip to Abu Dhabi to play an exhibition game had any impact on their exit.
City had 65% of possession and 24 shots at Etihad Stadium but fell behind to a goal from Chelsea loanee Patrick Bamford before Kike's second.
"We were nervous," said Pellegrini, whose team returned from the Gulf state late on Friday. "They are a team who work well, that's why they are second in the Championship. They had opportunities to score more goals and deserved to go through."
Boro boss Aitor Karanka told BBC Sport: "I can't find words to explain my feelings today. But I'm proud of the players, the crowd, the fans, the staff and the club. We could have won by more because we were very well organised and have quality up front."
|Premier League||Team||FA Cup status|
|5||Arsenal||STILL TO PLAY|
|7||West Ham||STILL TO PLAY|
|10||Stoke||STILL TO PLAY|
|15||Aston Villa||STILL TO PLAY|