Manchester United 1-6 Manchester City
Manchester City inflicted Manchester United's worst home defeat since February 1955 as they thrashed the champions in ruthless fashion to go five points clear at the top of the Premier League.
City were also the victors on that occasion 56 years ago, winning 5-0, but this visit was portrayed as a measure of their progress against the 19-time champions.
And Roberto Mancini's men could not have delivered a more emphatic statement as Sir Alex Ferguson's side were humiliated.
It was the first time United had conceded six goals at Old Trafford since 1930, when Huddersfield won 6-0 and Newcastle 7-4 within four days of each other.
City led just 1-0 at half-time, but the second half was completely one-sided and the eventual margin of victory could have been even more convincing.
Mario Balotelli, in the headlines for accidentally setting his house ablaze with fireworks, put City on their way with goals either side of the interval as United struggled to contain the array of attacking talent in front of them.
United were reduced to 10 men when Jonny Evans was sent off early in the second half but City's superiority was such that they looked on course for a landmark victory from the moment they took the lead.
Sergio Aguero added a third and, even though Darren Fletcher pulled a goal back, this only proved the signal for a late surge by City that brought three more goals and a result that will have sent shockwaves through the Premier League.
Substitute Edin Dzeko scrambled in a fourth and the magnificent David Silva ran clear to add another, before the Bosnian striker inflicted the final wound seconds from the end.
As Ferguson strode briskly towards the Stretford End at the final whistle, he will have been reflecting on the extent of the challenge now facing him from the club he once branded "noisy neighbours".
To increase United's pain, this was their first home defeat in any competition since April 2010, when they lost to Chelsea - but even that defeat, which effectively cost them the title, may not turn out to have the same long-term significance as this heavy beating.
United's stature is such that one result must not bring the immediate announcement of a shift in the balance of power in Manchester - but the swathes of empty seats around Old Trafford and the wave of attacks pouring towards David de Gea's goal in the second half emphasised that City quite simply have greater firepower and talent in their squad at present.
Mancini left Samir Nasri and Dzeko on the bench - but was still able to exploit a wide range of attacking options in Balotelli, Silva and Aguero.
In contrast to what was to come, City were barely allowed any time to settle on the ball in the opening exchanges, with Ashley Young prominent and drawing heavy fouls from Micah Richards and James Milner.
And it was against the run of play that City took the lead after 22 minutes, courtesy of a stroke of casual quality from Balotelli. Silva was the creator but Balotelli, given too much time and space by Evans, finished sublimely with a stroked finish into the bottom corner.
Balotelli, in recognition of those latest chaotic events in his personal life, then revealed a T-shirt bearing the slogan "Why Always Me?". Despite the evident good humour of the gesture, he was booked by referee Mark Clattenburg.
United's hopes of mounting a serious response suffered a blow within two minutes of the restart when Evans, who had endured a miserable afternoon, lost concentration and allowed Balotelli to steal in behind him. The defender's only reaction was to haul the Italian down, resulting in an inevitable red card.
The opportunity was there for City to overpower their arch-rivals and they accepted it as they went in search of further goals to emphasise their supremacy.
City doubled their lead on the hour with another superbly created goal finished by Balotelli. Silva cleverly played in Milner, who provided a cross that left the striker with the simplest of goals from close range.
Aguero had been quieter than his attacking colleagues but got in on the act after 69 minutes. The outstanding Milner played in Richards and, once again, a delivery across the face of the goal proved too much for United, Argentine Aguero arriving to complete the formalities.
Mancini then removed Balotelli and introduced Dzeko, who almost scored a fourth within seconds of his arrival, only to see his shot drift inches wide.
And, with United chasing a lost cause and leaving space at the back, Silva fired over from 10 yards and Dzeko forced a fine save from De Gea when he was set free by the Spaniard.
United refused to give up even in the face of impossible odds and Fletcher offered some hope when he pulled one back with nine minutes left, striking a fine rising shot from 20 yards that gave Joe Hart no chance.
It was a goal for which the phrase "false dawn" was invented. Dzeko took advantage of good work from Joleon Lescott to score the fourth before Silva got the goal he deserved with a composed strike.
And with some United supporters actually pleading with referee Clattenburg to put them out of their misery, one more moment of brilliance from the magical Silva found Dzeko surging into the area to finish left-footed for his second.