Manchester United and Manchester City left their tortured opponents and the Premier League in no doubt they are the teams to beat this season after hugely confident demolitions of Arsenal and Tottenham Hotspur on Sunday.

Champions United battered a depleted Arsenal 8-2 at Old Trafford with Wayne Rooney hitting a hat-trick and rampant City striker Edin Dzeko scored four in a 5-1 away rout of a shell-shocked Spurs.

The Manchester duo stormed to the top of the table with their third wins out of three after Chelsea and Liverpool, now two points back, had hit the summit on Saturday.

In contrast, north London's beleaguered Arsenal and Spurs sit towards the bottom after failing to win in the league this season.

"I think that we played a really good game against a Tottenham side that I think is a fantastic team," Manchester City manager Roberto Mancini told Sky Sports.

"I was sure that Dzeko this year could score lots of goals. I'm disappointed only for the goal we conceded.

"The season is very very long but it was important that we started the season well. The next game will be hard because everyone will think we can score three or four goals."

United carved a largely inexperienced Arsenal side apart from the start and it was no surprise when England's Danny Welbeck, who later went off with a hamstring injury, took advantage of poor defending to head in Anderson's scooped pass.

Goalkeeper David De Gea, who has suffered wobbly moments in his fledgling United career, made amends with a penalty save from Robin van Persie midway through the first half and his smile was broader when Ashley Young curled in a beauty.

Rooney bent home a perfect free kick as Arsenal keeper Wojciech Szczesny's goading backfired but De Gea made another slip on halftime when Theo Walcott's shot went in through his legs.

Another delightful Rooney special and a Nani chip followed after the break before Park Ji-sung and Van Persie traded strikes.

Defender Carl Jenkinson became the third Arsenal player in three league matches to be sent off and Rooney completed his treble with a late penalty before winger Young finished off the remarkable rout with another fine goal.

While United manager Alex Ferguson decided to stick with the youthful side which beat Spurs 3-0 on Monday and leave regulars Rio Ferdinand and Javier Hernandez on the bench, Mancini made changes such is the depth in his expensively-assembled squad.

Debutant Samir Nasri, who quit Arsenal along with Cesc Fabregas to leave troubled Arsene Wenger scrambling for players late on in the transfer window, was the architect of the first two City goals with Dzeko expertly converting his crosses.

The Bosnia forward, anonymous last term after a big move from VfL Wolfsburg, sealed his hat-trick from close range after the break before strike partner Sergio Aguero scored a clever fourth and Younes Kaboul pulled one back.

Spurs, beaten to a Champions League spot by the visitors last term, had decent chances but the gulf in class was clear.

Chelsea target Luka Modric was booed by his own Spurs fans after his transfer request and their mood darkened further when Dzeko bent in his brilliant fourth in injury time.

In the other Sunday matches, striker Leon Best scored twice in Newcastle United's 2-1 home win over Fulham and Stoke City's Ryan Shotton struck late in a 1-0 victory at West Bromwich Albion.