City, without suspended former Hammers striker Carlos Tevez, dominated from kick-off, and it was no surprised when Yaya Toure rifled in the opener on the half-hour mark.
The home side rallied after the break and had appeals for a penalty turned down for handball against Yaya Toure.
However, the Ivory Coast midfielder then helped the visitors double their lead when his shot hit the post and went in off goalkeeper Robert Green, before substitute Adam Johnson wrapped things up with nine minutes left.
James Tomkins headed in a late consolation for the Hammers, who face a real battle for survival in 2011.
Source: PA
Source: PA