The home side's delirious fans mocked Arsene Wenger with chants of "You're getting sacked in the morning" as Rooney walked off with the matchball, having scored his 150th Red Devils goal, then adding two more after half-time to complete his hat-trick.
Yet Rooney's efforts did not even account for half of United's staggering tally as they scored eight for the first time since 1999.
Danny Welbeck, Ashley Young, Nani and Park Ji-sung also found the net before Young completed the rout with his second.
It was Arsenal's worst ever defeat against United and the first time they have conceded eight in a league game since 1896.
The result leaves Wenger staring at the biggest crisis of his 15 years at the helm.
For Sir Alex Ferguson, so strident in his defence of the Frenchman pre-match, this is of little concern.
His side are yet to drop a point, as are their noisy neighbours across the city.
And while there are plenty at Stamford Bridge and Anfield who will strongly disagree this season already seems to be turning into an eight-month shoot-out between the red and blue halves of Manchester.
That United suffered a series of setbacks during the first-half just made the 3-1 interval scorline even more remarkable.
Jonny Evans conceded a penalty, Welbeck limped off with a hamstring injury and Theo Walcott scored.
None of this prevented Ferguson's side jogging off to a rapturous reception after a mesmeric display, in which their youngsters again showed their class, and even David De Gea joined the party.
Derided for his performances since an £18million summer move from Atletico Madrid, De Gea needed a lift. Turning Robin van Persie's penalty round the post provided it.
It was the central component of a pivotal five-minute spell, during which United established their clear superiority.
The hosts had already threatened to dismantle an Arsenal side shorn of Bacary Sagna and Thomas Vermaelen, in addition to the suspensions of Alex Song and Gervinho.
But when Anderson lifted the ball over Arsenal's static defence, Welbeck had too much strength for Johan Djourou and headed over Wojciech Szczesny.
In their present fragile state, Van Persie's failure to punish Jonny Evans' penalty box foul on Walcott was a shattering blow.
That United immediately headed up to the other end and doubled their advantage through Young's magnificent curling strike only made matters worse.
Even Welbeck's injury, which will surely deprive England of his services in Bulgaria next week, was only a minor inconvenience, especially as his replacement was last season's star man Javier Hernandez.
Rooney added his name to the scoresheet with a perfect free-kick, which beat Szczesny's despairing grasp to find the top corner.
Walcott pulled one back in stoppage time for the visitors but when Young forced Szczesny into an excellent save by his near post straight after the restart, Arsenal's fans could sense what was unfolding and launched into long and passionate backing of their team.
It wasn't that Arsenal were incapable.
Had Van Persie's first-time volley found the net instead of being superbly repelled by De Gea or Andrey Arshavin's close-range effort not flicked wide off Evans, they would have been back in with a chance.
They were incapable of preventing United from swarming all over them though.
The heroic Szczesny denied Young. Nani contrived to miss from four yards. It was all rather embarrassing for the visitors, who simply could not hold out.
When Johan Djourou pulled Rooney down on the edge of the area, he was merely creating the opportunity for England's number one striker to replicate his landmark United goal with his 151st.
Rooney then sent Nani through, the Portugal winger calmly chipping Szczesny before making way for Park Ji-sung, who promptly grabbed one himself.
Van Persie pulled one back amid the carnage, which also saw Carl Jenkinson sent off for hauling down Hernandez, having already been booked.
At that stage, Arsenal would happily have accepted the final whistle.
But their agony was far from being over.
After Van Persie has scored, Walcott pulled one back, which merely seemed to annoy their hosts.
Evra was brought down by Walcott, allowing Rooney to complete his hat-trick from the spot and then, in stoppage time, Young added an eighth.
The scoreboard told its own story at the final whistle.
United will march on to face the threat posed by Roberto Mancini and his men.
For Wenger, there are far more searching and deep-rooted questions that, in the wake of the departures of Cesc Fabregas and Samir Nasri, may not be easy to answer.