From being eight points adrift and apparently in chaos following that loss at Arsenal, City have reeled off four straight wins, whilst United have managed just one victory.
It has given the Blues the ascendancy, which even Silva conceded was unlikely as he left the Emirates.
"There was never a point when we totally gave up on the league but we did get to a point when we knew it was very difficult," he said.
"All we could do was keep working and get three points after three points.
"I am surprised to see United taking an eight-point lead and then giving it up but don't forget we had a massive lead and lost it. It's a very long and competitive season and now we are here we have to finish the job."