A powerful display from Manchester City condemned Manchester United to a 4-1 defeat in a chastening local derby for the Barclays Premier League champions.
Sergio Aguero’s superb opener put the hosts in the ascendancy after 16 minutes, and Yaya Toure’s close-range goal in first-half injury-time left the Reds - shorn of the injured Robin van Persie - struggling to retain a foothold in the game.
That perilous position was compounded by a disastrous opening to the second half, as City struck twice in five minutes, again with slack marking playing a part in United’s demise as Aguero and Samir Nasri were given time and space to beat the exposed De Gea.
Pride smarting and with City increasingly inclined to sit back on their advantage and look to strike on the counter-attack, United showed greater purpose thereafter and began creating chances.
However, City’s defence was as obdurate as its midfield and attacking counterparts were incisive, and the Reds' only consolation came when Wayne Rooney curled home a magnificent 87th-minute free-kick.
David Moyes’ side had been condemned to a second defeat of the season long before that point, though, and now must quickly switch their sights to Wednesday’s Capital One Cup clash with Liverpool.
Beyond that, next Saturday brings the league visit of West Bromwich Albion to Old Trafford, and a chance for the champions to emerge positively from a taxing start to the defence of their title.