By Ewan Murray Chelsea face the toughest test of their pre-season tour to date when they take on Premier League champions Manchester City in the United States this Saturday. The Blues made a disappointing start to the Enzo Maresca era following a 2-2 draw with League One Wrexham and a 4-1 demolition at the hands of Glasgow outfit Celtic. However, they somewhat redeemed themselves in their third pre-season outing, beating Mexico’s Club America 3-0 thanks to two penalties and a Marc Guiu strike. Man City’s poor start to pre-season can be mitigated by their lack of available first-team players. T…