Manchester United dealt Manchester City's Champions League qualification hopes another blow by storming back from behind to trounce their derby rivals 4-2 in the Premier League yesterday. Sergio Aguero gave City an eighth-minute lead at a blustery Old Trafford, but United hit back through Ashley Young, Marouane Fellaini, Juan Mata and Chris Smalling to register a sixth successive league win.Aguero claimed another goal but it was too late to prevent United ending a sequence of four consecutive defeats against their neighbours.The win gave United a four-point cushion over City in third place - the last automatic Champions League qualifying spot - and took them back to within a point of Arsenal ahead of next weekend's home game with leaders Chelsea.City have now lost six of their last eight games in all competitions, and manager Manuel Pellegrini is likely to face renewed questioning about his ability to revive the team he steered to the title a year ago.It was a fourth successive away league defeat for City - their worst run since 2006 - and hammered another nail in their title defence, leaving them 12 points behind Chelsea having played a game more.Liverpool can close to within four points of City by beating Newcastle United today.In the earlier game, Chelsea won 1-0 away to QPR, scoring with their only shot of the match. ..