Man City outclass United
Arsenal go on top of the table with smooth win
Aguero volleyed City ahead after 16 minutes and made it 3-0 in the opening minute of the second half after Yaya Toure had put the home side in command on the stroke of half-time. United's defence was sliced wide open again when Samir Nasri volleyed home after 50 minutes and manager David Moyes's first Manchester derby descended into a nightmare.
Wayne Rooney's curling free-kick was the only ray of sunshine for United, who have now lost four of the last five league derbies with City who climbed to third in the table with 10 points, two behind leaders Arsenal and Tottenham Hotspur. United are in eighth place with seven points from five matches. Arsenal climbed on top of the the table with a smooth 3-1 win over Stoke City.
The big screen at the Etihad had showed a re-run of the goals from City's 6-1 thrashing of United at Old Trafford two seasons ago, when the team from the blue side of the city went on to win the title, and those visions seemed to set the tone. United already started the day badly when striker Robin van Persie was ruled out with a groin strain and it got worse as last season's runners-up City trampled all over them from the start.
The Arsenal fans came to acclaim record signing Mesut Ozil on his home debut but Aaron Ramsey took the plaudits with the first goal in a 3-1 win over Stoke which put the Gunners top of the Premier League. Welsh midfielder Ramsey scored his seventh goal of the season after five minutes, firing home after Ozil's free kick had come back off Stoke keeper Asmir Begovic.
Stoke did equalise after 26 minutes through American Geoff Cameron but goals from Per Mertesacker and Bacary Sagna sealed a seventh consecutive win in all competitions for the Gunners.
After losing their opening match of the season at home to Aston Villa, Arsene Wenger's side have won four league games in a row and have 12 points, two more than Chelsea and Liverpool. Swansea City followed up a notable 3-0 Europa League win in Valencia in midweek with a 2-0 victory at Crystal Palace that moved Michael Laudrup's side into mid-table.
While Ramsey continued his hot streak, Ozil offered Arsenal fans plenty of encouragement, having a hand in all three goals. It was the German playmaker's ball into the area that allowed Mertesacker to direct a header in at the far post after 36 minutes and he then supplied the second-half free kick which Sagna met with a looping header over the stranded Begovic.
Stoke had threatened to sour the mood when Cameron steered in a rebound after Marco Arnautovic's shot rebounded off the post and enjoyed decent spell after the break before Sagna ended their hopes of a rare away point against Arsenal.
City barely missed David Silva, who had not recovered in time from a thigh injury, with the nippy Jesus Navas, Samir Nasri and Sergio Aguero posing United problems with every push forward.
The hosts' dominance was soon rewarded. Nasri shook off Chris Smalling down the left and his flick found Aleksandar Kolarov whose accurate cross was deftly volleyed home by Aguero to send home fans wild on a warm afternoon in Manchester.