MANCHESTER, England (Reuters) – Kevin De Bruyne and Riyad Mahrez both scored twice as Manchester City restored their lead at the top of the Premier League to six points with a 4-1 derby victory over Manchester United at the Etihad Stadium on Sunday. United had put up a decent fight in the first half, going in 2-1 down at the break, but City’s quality showed after the interval with Ralf Rangnick’s side looking increasingly demoralised. City have 69 points from 28 games with Liverpool on 63 from 27 matches. United slip down to fifth place, a point behind Arsenal who beat Watford on Sunday and ha…