Rooney meledak pada minit ke-40 dan 62, kedua-duanya menerusi sepakan percuma di luar kotak penalti sebelum melengkapkan hatrik pada minit ke-81.United memperoleh gol awal menerusi Danny Welbeck pada minit ke-21 sebelum Asley Young meledak pada minit ke- Theo Welcott menyamakan kedudukan pada minit ke-27. Theo Walcott kemudian menyumbat masuk pada minit ke-48.
Masuk separuh masa kedua Nani meledak pada minit ke-65 disusuli Park Ji Sung pada minit ke-69 sebelum Robin Van Persie memperoleh gol kedua Arsenal pada minit ke-73.
Young sekali lagi merembat jaringan pada minit ke-90 untuk melengkapkan kemenangan bersejarah United 8-2.
Just hours after neighbours Manchester City had inflicted a 5-1 hammering on Tottenham at White Hart Lane, United ensured a double dose of Mancunian misery for north London’s embattled rivals by maintaining their 100 per cent start to the season.
But for David de Gea’s first-half penalty save from Robin van Persie with the scoreline at 1-0 to United, the outcome could have been so different for Wenger’s young team.
Yet United, fielding the same youthful team which defeated Tottenham 3-0 last Monday, showed that inexperience combined with old heads can bear fruit.
The only downside for United was the first-half injury to Danny Welbeck, whose hamstring strain looks certain to force him out of England’s forthcoming Euro 2012 qualifiers against Bulgaria and Wales.
Welbeck had set United on their way to victory, however, by netting his second goal in a week to open the scoring,
The 20-year-old, capped by England against Ghana last season, held off the less than muscular challenges of Johan Djourou and Laurent Koscielny to head Anderson’s lobbed pass beyond the statuesque Wojciech Szczesny on 22 minutes.
Arsenal responded well, though, and referee Howard Webb correctly awarded a penalty to the visitors on 27 minutes when Jonny Evans’s tug on Theo Walcott sent the winger tumbling to the ground.
Van Persie was foiled by De Gea, however, with the Spanish goalkeeper diving low to his right to keep out the Arsenal captain’s spot-kick.
Having endured a tough start to life in English football, the reaction of De Gea’s team-mates, who raced to congratulate the 20-year-old, suggested a turning point for the youngster.
It was certainly a turning point for United. Having faced an early equaliser, they punished Arsenal for the penalty miss by making it 2-0 through Ashley Young just one minute later.
And it was a stunning goal from the former Aston Villa winger, a 20 yard curler which left Szczesny with no chance.
The Pole should have done better with Rooney’s first, however, when the United forward beat him with a free kick on 41 minutes.
It was a well-executed free kick, but the ball was within the keeper’s reach and he should have pushed the shot to safety.
Arsenal started brightly in the second-half, however, and it required a fine save from De Gea to keep out Van Persie’s near post volley on 53 minutes.
Once again, though, United responded to Arsenal missing a chance and they made it 4-1 eleven minute later when Rooney netted another free kick after being fouled by Djourou.
Rooney’s second signalled a goal-rush. Nani made it five three minutes later after latching onto Rooney’s pass before Park Ji-sung claimed a sixth on 70 minutes.
Van Persie scored a consolation goal to make it 6-2 on 74 minutes, but defender Carl Jenkinson was sent off for a second yellow card two minutes later, leaving Arsenal vulnerable to further United goals.
And the seventh came on 81 minutes when Rooney scored from the penalty spot after Walcott had fouled Patrice Evra.
To make matters worse for Arsenal, Young scored United’s eighth in stoppage time to claim top spot in the Premier League.
Joy for United, absolute agony for Arsenal.