Manchester City's wait for the Premier League title goes on after surrendering a lead to lose 3-2 to Manchester United.
A victory would have confirmed Pep Guardiola's men as 2017/18 champions and it looked to be the case as Vincent Kompany and Ilkay Gundogan put them two up in the first half.
United were as big as 150/1 with Sky Bet in-play, as City went 1/50 to see out the win they needed to take the title with their main rivals in attendance.
Paul Pogba, who Guardiola claimed he was offered in January, scored twice in three minutes to draw United level and stun a packed Etihad crowd.
Chris Smalling then volleyed home to complete the comeback, before a stunning save by David De Gea denied Sergio Aguero an equaliser in the closing stages of the thrilling derby.
It surely remains only a matter of time before City, who are still 13 points clear, take the title but the manner of the loss so soon after Wednesday's Champions League defeat at Liverpool asks questions of them.
Early on, City fed off a raucous atmosphere as United's attempts to play more openly than they did in their December derby loss played into the hands of the hosts.
Ashley Young twice got the benefit of the doubt from referee Martin Atkinson, first after the ball struck his arm and then following a clash with Raheem Sterling.
Sterling repeatedly troubled the United defence and he played in David Silva, who fired over, and Bernardo Silva, who failed to get away a clean shot.
The opener came from a corner in the 25th minute as City captain Vincent Kompany ignored the shirt-pulling of Chris Smalling to reach Leroy Sane's cross and power a header past David De Gea in trademark fashion.
The second followed quickly as Ilkay Gundogan combined with Sterling and then brilliantly turned away from Nemanja Matic to poke a shot into the bottom corner.
Further chances came thick and fast as City found their groove. Sterling spurned three more opportunities before the break as he twice shot over after breaking clear and then hit another drive at De Gea. David Silva missed another opportunity and De Gea saved a Gundogan header.
Gundogan hit a post early in the second half but United, with the blue-haired Paul Pogba coming to the fore after a dismal opening period, finally woke up.
Pogba first had a sighter as he forced Ederson to save low down. He then pounced from close range to reduce the arrears after Ander Herrera had chested down an Alexis Sanchez cross.
That appeared to inspire Pogba, who moments later equalised as he raced on to another Sanchez cross to head past Ederson.
City tried to regain control but they allowed their concentration to slip and as Sanchez delivered a free-kick into the area, Smalling got ahead of Kompany and volleyed home to put United ahead.
City quickly sent on Kevin De Bruyne and Sergio Aguero to retrieve the situation and the latter was aggrieved not to have been awarded a penalty after going down under a robust and clumsy Young challenge.
Tempers from both sides flared in the aftermath but United were to have their day with De Gea saving late on from Aguero and Sterling having another effort cleared off the line.
Post-match reaction
Pep Guardiola remained philosophical amid the obvious disappointment of Manchester City's derby defeat.
"Of course, we wanted to win today," City boss Guardiola said. "I am not going to deny that, but we know exactly which team we play.
"They are second in a good league, but I am here to try and analyse the feelings.
"I am sorry for the fans, but I don't think they can have complaints about what we have done.
"When you analyse the game, it was good, so I cannot expect 30 minutes and the opponent doesn't do absolutely anything.
"My dream is happening in the first half, when we didn't concede one shot on target.
"But they have pride, a good manager and maybe in half-time he said 'oh guys, we've got to do something more'.
"But we ran, we fought, we did everything, so in one month, two month or one or two years and we'll see the game and say 'wow, how could we lose that game?'
"But we lost it so for the fans it's hard, but maybe we're going to get more credit if we are able to win the Premier League 'OK, how tough it was'.
"People since November, December say 'the Premier League is done', 'the Premier League is done', 'the Premier League done', and it was a tough fight to keep going every single weekend, to be focused because it's not done.
"And, of course, now it is not done, so the people say, 'you're going to win'. Wait. In football everything can happen.
"It's the first time we've lost two games in a row this season and now we have to recover, try again, come back to basics and win games. We're going to try next Tuesday and next games."
Manchester United boss Jose Mourinho was surprisingly magnanimous given the derby outcome and Guardiola's controversial pre-match comments about Paul Pogba.
"I told my midfield players that they didn't need to improve because they were playing very well, even in the first half, all of them," the United boss said.
"I think it's very difficult to be a midfield player against Manchester City and Paul, Ander (Herrera) and (Nemanja) Matic were playing really well, but I needed more from (Jesse) Lingard and Alexis (Sanchez).
"I need them to connect our good football in midfield, and especially I need my defenders to be more confident because with just a little bit of pressure by City, they were kicking the ball, they were nervous and not bringing the ball with quality to my midfielders.
"I needed improvement in terms of confidence of the defenders, also to bring the line-up so we could lose the ball and press a little bit.
"And then it was about keeping confidence. Sometimes you are losing, and the instinct is to change immediately because you don't like anything."
Follow Sporting Life on social media - find us on Facebook here or tweet @SportingLife
Last updated at 1920 BST 07/04/2018.