Paul Pogba scored twice before Chris Smalling poked in a 69th-minute winner as Manchester United came back from 2-0 down at half-time to beat champions-elect Manchester City 3-2 at the Etihad Stadium on Saturday evening.
A thunderous Vincent Kompany header and cool Ilkay Gundogan finish in the 25th and 30th minutes promised to clinch the Premier League title for the Citizens in record time against their city rivals.
The visitors came out firing after the break though, and two Pogba goals in the space of three minutes levelled the score before Smalling's winner earnt the Red Devils victory in the 176th Manchester derby.
The teams entered the pitch to a thunderous ovation from both sets of fans, understandable with what was on the line, before a minutes applause was held for the late Ray Wilkins, who passed away on Wednesday.
Both teams expectedly up for it
United adopted a high pressing style to combat the hosts' on-the-ball brilliance, but it was City applying the pressure on the opposition goal right from the get-go.
There were penalty appeals in just the fifth minute after David Silva broke free down the left wing and fired a low cross towards the box, a cross which struck the hand of Ashley Young who had slipped. Referee Martin Atkinson, arguably incorrectly, waved the claims away.
Jose Mourinho's side had a chance to put the ball into their target men on 15 minutes after Danilo took out Paul Pogba on the left, but Alexis Sanchez' free-kick was wastefully lobbed into the arms of Ederson.
Pogba then clumsily lost the ball to David Silva in space 30 yards from David de Gea's goal but was let off as the Spaniard burst forward and sprayed his ranged effort high and wide.
The United goalkeeper was called into action for the first time on 22 minutes. Fancy footwork by Raheem Sterling on the edge of the box led to the ball trickling its way through to Bernardo Silva and he had his point-blank poked shot blocked by the no. 1.
Quickfire double puts City in control
Just as it seemed the visitors were becoming more comfortable, City captain Kompany came up with a moment reminiscent of one he produced in the same match in April 2012 to put the Citizens ahead.
The Belgian defender emphatically defeated Chris Smalling in the air, again, to connect with Leroy Sane's corner from the left and power the ball past the hopeless de Gea to lift the roof off of the Etihad Stadium.
His goal in the 2011-12 season helped City claim their first ever Premier League triumph and that header sent Pep Guardiola's men directly towards their third.
Five minutes later, on the half-hour mark, the home side's lead was doubled by Gundogan to move them even closer towards a fifth top-flight trophy.
A rare error from de Gea saw his poor clearance start a devastating City attack and the Turkish midfielder finishing slick link-up between Bernardo Silva and Sane by turning in the box and cooly slotting into the bottom right corner. That was when the party truly begun in the stands.
It so nearly was, and should've been, a third for the champions-elect immediately afterwards, but Sterling widely blazed over the crossbar after being sent through one-on-one with the United 'keeper.
Wasteful Sterling can't punish before break
The chances for City to make it an even more humiliating day for their city rivals kept on coming as half-time approached. David Silva picked up the ball on the left flank and threaded a pin-point pass across the area, which Sterling once again lifted over the bar with just de Gea to beat.
Ander Herrera was handed the first booking of the game in the 38th minute after hacking down Fernandinho in a pointless position, before Romelu Lukaku was also rescinded in stoppage time for a late challenge on Kompany.
Sterling had another opportunity to add to the scoreline in between after Sane worked space on the left again and found the Englishman unmarked on the penalty spot, but his shot was straight at the goalkeeper.
United quick out of the blocks after interval
After such dominance by City throughout the whole of the first half, in which United couldn't even conjure up a shot, Jose Mourinho's half-time dressing room dressing down looked like it worked wonders as the game was to quickly turn on its head.
Pogba looked to profit from two United corners within the first five minutes and the ball eventually fell to the Frenchman from 25 yards out, leading to him test Ederson for the first time in the match with a powered, low strike.
Gundogan almost added a second on 51 minutes as he clipped the bar with a curling strike before the away side started the most unlikely of comebacks down the other end.
Bright play by Alexis Sanchez down the right led to the Chilean finding Herrera on the edge of the City box. His delightful chested pass sent Pogba through on goal, who did well to loft the ball over the rushing Ederson from a tight angle to get United right back into proceedings.
That goal seemed to catch the hosts off-guard as they suddenly looked awfully vulnerable at the back after not being tested at all before that piece of action, and it was only two minutes later when Pogba bagged his second to draw United level.
The danger came from Alexis on the wing again as he clipped in a terrifically precise cross into the box which the Red Devils' no. 6 snuck in behind the defensive line to nod in past Ederson. All four goals had been scored in front of the away supporters and they were in completely different spirits after that went in.
Smalling turns from foe to hero
David Silva missed an opportunity to restore City's lead with an hour gone, aiming a shot straight at de Gea at his near post, before Lingard stroked an attempt just past the post for the away side right down the other end. An exhilarating final 30 minutes was well and truly in store; end to end stuff at its finest.
In the 69th minute, the unthinkable happened as Chris Smalling redeemed himself for his error for City's first in the best possible way by completing a stunning comeback.
Alexis was the provider once again, swinging a free-kick in behind the Citizens' defence to find the marauding centre-half who poked an unstoppable volley past Ederson to cue incredible scenes. Premier League at its sparkling best.
Pep Guardiola responded to going behind by introducing the originally-rested Gabriel Jesus and Kevin De Bruyne, changes he would've hoped he wouldn't have to make ahead of the crunch Champions League clash with Liverpool here on Tuesday. That was before Sergio Aguero made his return to action in what was a last throw of the dice.
Young lucky not to give away late penalty
Ashley Young was very lucky not to concede a penalty again in the 78th minute. He recklessly lunged into Aguero inside the box but Martin Atkinson deemed it a fair tackle. That was before a coming together fit for the Manchester derby after Fernandinho's late challenge on Jesse Lingard.
The Brazilian recieved a yellow card, as did Aguero for complaining about the penalty decision, before Pogba was next to go into the book for a horrendous tackle on Nicolas Otamendi from behind.
Jose Mourinho helped the clock run down by introducing both Marcus Rashford and Scott McTominay in the final 10 minutes before 'squeaky bum time' really kicked in for the visitors.
David de Gea pulled off, well, a David de Gea stop to deny Aguero, who flicked on a Sane cross from the left with his head which the Spanish 'keeper had to push over the bar with one hand. The action kept on coming at United's end, and woes in front of goal continued for Raheem Sterling.
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United hold on for massive result
After repeated corners, the young winger found himself with the ball at his feet inside the six yard box but incredibly hit the post with his shot. In that moment it seemed destined that it wasn't City's day to secure Premier League success.
During five minutes of added time, Danilo, Kompany and Jesus were all booked for what looked like desperation fouls and Mourinho replaced Herrera with Victor Lindelof. Then, the full-time whistle was blown.
The result doesn't just delay Manchester City's title party today, but it means they can't even secure the crown in their next league outing against Tottenham Hotspur at Wembley next weekend - they need two more wins.
Smalling's winner inflicted back-to-back defeats on a Pep Guardiola team for the first time in almost three years, and ended a 27-home game unbeaten run for the Citizens, as well as a 14-match winning run at the Etihad.