Pep Guardiola said he cannot find the solution to Manchester City's dreadful run after Manchester United struck twice in the final two minutes to win 2-1 at the Etihad on Sunday.
City have won just once in their last 11 games, a run that includes eight defeats.
Josko Gvardiol's first-half header had put Guardiola's men in front.
But United hit back for just Ruben Amorim's second win in five league matches since taking charge last month.
Bruno Fernandes' penalty levelled before Amad Diallo squeezed home the winner from a narrow angle in the last minute of regular time.
Defeat leaves City still in fifth, nine points off leaders Liverpool, who have a game in hand.
"I don't have defence, I'm the boss, I'm the manager. I have to find a solution and I don't find a solution," said Guardiola.
BOLD CALL
"This is a big club, when you lose eight out of 11, something wrong is happening.
United climb to 12th and within five points of their city rivals.
The Red Devils will be hoping a dramatic victory can also be the starting point for Amorim to turn around the momentum of a rivalry that City have dominated over the past decade.
"I think for the fans it has a deep meaning, especially in this context, in this moment," said Amorim after his first taste of the Manchester derby.
"We had a difficult moment one week ago against Nottingham (Forest) at home with a storm. It was a really tough moment after the game. Today, we are more happy, but it's three points that we have to continue."
Amorim made a bold call before kick-off as both Marcus Rashford and Alejandro Garnacho were left out of the United squad with the Portuguese saying "we have to put the standards really high" on and off the field.
A shortage of confidence in both sides was clear to see in a game short of quality until a dramatic finale.
United's set-piece defending has been at the root of their poor start to life under new management.
For the third consecutive Premier League game they conceded from a corner as Kevin De Bruyne's deflected cross looped perfectly into the path of Gvardiol to head in on 36 minutes.
A slow burn of a derby finally came to life seconds later when Kyle Walker and Rasmus Hojlund went head-to-head with both ending up getting booked.
United did not manage a single shot on target in the first 45 minutes and Amorim was growing visibly frustrated at his side's poor play on the ball as the second period started in a similar manner.
A vintage City side under Guardiola would have put their neighbours to the sword, but English champions created nothing of note in the second period.
Diallo finally forced Ederson into action with a header that the Brazilian clawed around the post on the hour mark.
Fernandes then missed a glorious chance to equalise 15 minutes from time when his dink over Ederson drifted wide with just the Brazilian to beat.
However, City were to be the architects of their own downfall.
Matheus Nunes' short backpass played in Diallo, who was then chopped down by the Portuguese midfielder in his desperation to atone for the original error.
Fernandes this time coolly sent Ederson the wrong way to level.
City's defence was then undone by one simple long ball over the top by Lisandro Martinez that Diallo raced onto, rounded Ederson and kept his composure to find the net.