The Red Devils produced a customary display, bouncing back from their 2-2 draw with Newcastle United last week.
Wayne Rooney, who had not scored in the 13 appearances for both club and country, broke his drought when he sent Hammers keeper Robert Green the wrong way from the penalty spot after Jonathan Spector had brought down Ryan Giggs in the area in the 33rd minute.
That lead was doubled when Portuguese winger Nani beat off competition from Danny Gabbidon before scoring past Green in the 50th minute and the victory was complete when Dimitar Berbatov produced a spectacular airborne volley after a neat Nani cross with just over 20 minutes remaining.
The win pushed Man United to third on the table with two wins and a draw whilst West Ham slumped to their third successive defeat to fall to the bottom.
MU Edwin van der Sar (gk), Jonathan Evans (Smalling 74'), Nemanja Vidic, Patrice Evra, John O'Shea, Paul Scholes (Carrick 74'), Darren Fletcher, Ryan Giggs, Nani, Dimitar Berbatov (Owen 74'), Wayne Rooney
WHU Robert Green (gk), Matthew Upson, Danny Gabbidon, Herita Ilunga, Jonathan Spector, Scott Parker, Mark Noble, Luis Boa Morte (Stanislas 90'), Kieron Dyer (Piquionne 76'), Julien Faubert (Barrera 62'), Carlton Cole