Manchester United surged five points clear of their city rivals with a 2-0 beating of Blackburn Rovers at Ewood Park.
Late goals from Valencia and Young were enough secure all three points and in so doing placed one hand on their 20th league title with second place Manchester city certainly having too much to do with seven matches remaining.
Valencia fired past Robinson from the right inside the far post with Robinson looking attached to his near post and stunned as ball flew into his net beyond his right sided dive.
Young got his goal perfectly placed – on the turn – and after making good space for himself to his right sent a shot straight down the inside of the upright with the keeper having no chance at a save.
Manchester City had dropped two valuable points on Saturday after a come-from-behind 3-3 draw with Sunderland with Balotelli getting a brace.
The results leaves Mancini mourning the dip in form at City at the crucial time when momentum becomes a key factor for the remaining games.