Manchester United won at Manchester City to increase their lead at the top of the table thanks to Robin Van Persie's injury time winner at the Etihad Stadium.
This was the first Manchester derby since City's injury time comeback against QPR in May to lift their first Premier League silverware in 44 years and, perhaps just as importantly, snatch the title away from United.
Wayne Rooney's first half double give United a 2-0 half time lead. After a third from Ashley Young was incorrectly ruled out for outside, City fought back to 2-2 through YaYa Toure and Pablo Zabeleta and looked set to earn a point. But Van Persie's free kick in the second minute of injury time sealed three points for Sir Alex Ferguson's men.
One of the big talking points before the game was Mario Balotelli starting up front with Argentine striker Sergio Augero rather than the much favoured Carlos Tevez.
City made the dominant start, pressing their visitors consistantly and at one point had 76 per cent possession in the opening stages. Knowing the Red Devils' weakness was defending set pieces, as evident in their 4-3 victory at Reading last saturday, corners were easy to come by in the United box early on.
After much pressure on the visiting goal, Zabaleta did well to keep the ball going out for a goal kick and found Balotelli who took a horrible first touch and sent the ball blazing over. And that would come back to haunt them just minutes later.
On 15 minutes, completely against the run of play, Wayne Rooney ran past three City defenders and produced a cheeky finish which trickled past City keeper Joe Hart and into the bottom left corner.
The goal seemed to lift Ferguson's team and started to pressure their hosts, always looking dangerously likely to score a second.
Things went from bad to worse for City as Roberto Mancini was forced into making a substitution with 20 minutes gone. Influential captain Vincent Kompany came off with an apparant groin injury and was replaced by Kolo Toure.
Augero serged his way past the United defence only to produce a lacklustre shot with De Gea easily saving the attempt.
If City fans hoped they could get back into the game, they were to be proven wrong as on the 28 minute United broke forward again. After a good run on the flank, Rafael found Rooney unmarked in the box and was clinical enough to beat Hart again to seemingly give United daylight in the match.
City desperately tried to press forward in the last 15 minutes but in reality the majority of the first half was a convincing performance by the visitors.
Five mintues into the second half, Mancini took off Balotelli and brought on Tevez, who almost made an istant impact by adding speed to City's weak attack and passed through to frenchman Simar Nasri and David Silva, both of whom were offside.
After Ashley Young found the back of the net with an rebounded effort which was deemed offside, the home fans were finally given something to cheer.
Just before the hour mark, De Gea made a very good double save and after Tevez was blocked, YaYa Toure kept his cool from inside the penalty area to give City the goal they badly needed.
United were then keen to keep possession and try to slow the tempo down in an attempt to see out the game.
But on 78 minutes David Silva from extremely close range shot at goal and the ball took a deflection of De Gea and off the crossbar for a corner.
With seven minutes of normal time remaining, Mancini brought on Edin Dzeko who has been branded a super substitution and with good reason; he has scored nearly every time he has come off the bench.
But despite Dzeko almost making an immediate impact, City had struggled to break through a stubborn and well disciplined United defence and with the clock ticking down the home fans' anxiety grew even more.
But the Etihad Stadium then exploded with delight as an 85th minute corner from Tevez was headed away by Van Persie. But the ball found Zabeleta whose finish found its way past a crowded penalty area and into the bottom left corner to get City level.
A point was probably what City deserved for their second half display and the match looked set for a draw. However the match was to take another dramatic twist.
Tevez brought down Rafael on the edge of the area to set up the freekick. Van Persie, with the help of a slight deflection from Nasri, scored as the ball found its way past the helpless Hart and to break City hearts.
It was a conclusion to an outstanding second half which was end-to-end and what gives Sir Alex Ferguson the derby win he craved to give his team a six point lead at the top of the Premier League table.