Arsenal are Manchester City's biggest rivals for the Premier League title
With champions Chelsea needing an unprecedented run of results just to finish in the top four and Manchester United failing their first major title test, it appears that Arsenal will pose the biggest threat to City. That the Gunners are on the verge of a premature Champions League group stage exit could also allow them to focus on lifting domestic silverware.
United are leaden in central midfield
Arsenal were fired up, with Francis Coquelin pressing hard and Santi Cazorla influential. But United's midfield, which included Wayne Rooney in a central, attacking role in the first half, appeared to be wading through treacle.
Pace without the ball is hardly a strong point of Bastian Schweinsteiger and Michael Carrick - or, increasingly, Rooney. But it was the speed with which they moved the ball, especially in the first half, that was ponderous.
United manager Louis van Gaal's Plan B was to thicken up the midfield with the half-time introduction of Marouane Fellaini, and to move Rooney out left, but there was never any caution cast to the wind.
Alexis Sanchez lights up the Emirates
Arsenal's player of the season last time out started the campaign a little slowly, in the wake of his Copa America-winning exploits with Chile over the summer. But the rhythm is now back as he followed up his hat-trick at Leicester City the previous weekend with a beautiful brace. The first goal was a celebration of technique, the second a vicious thump - and he bristled with menace and intensity throughout the game. Arsenal need their talisman to be at the top of his game. The only worry was that he appeared to be holding his groin when he was substituted.
Anthony Martial the only positive for United
The 19-year-old striker's first touch and acceleration serve to quicken the pulse and instil worry in his would-be defensive shacklers, while there was also evidence of his strength and awareness.
He rolled Per Mertesacker, took a wonderful touch and was only denied by Petr Cech at the end of the first half. Martial has pace to burn, as shown when he got to the bye-line before Hector Bellerin to cross on 27 minutes. He looked like United's only attacking hope.