A debut goal from new boy Bobby Zamora sparked a Hammers fightback after strugglers Bradford City gave them a first-half scare.
The relegation haunted home side stunned Alan Pardew's promotion hopefuls with a rare goal from veteran Peter Atherton, but Zamora's header and a late strike by Marlon Harewood sealed another three points for the Hammers.
Atherton, who last netted in March, put his injury-plagued year behind him to raise hopes of a shock victory only for the Bantams to run out of steam as the visitors piled on the pressure.
City pressed from the kick-off and it took a superb early save by Stephen Bywater to deny Bradford's striker Alun Armstrong.
The on-loan Ipswich man got free inside the visitors box after just four minutes but his eight-yard header from Nicky Summerbee's corner was brilliantly pushed away by the Hammers keeper.
Armstrong then wasted a gilt-edged chance after a surging run from midfielder Gareth Farrelly.
After the ball bounced kindly into Armstrong's path he was left one-on-one with Bywater, but the keeper did enough to block his shot with his legs.
Armstrong saw a long-range effort fire wide before City's hard work got its reward with Atherton's 35th minute strike.
Scottish international Andy Gray did well to retain possession and when he laid the ball back the experienced midfielder coolly curled his shot beyond the grasping Bywater.
Just before the break, West Ham's liveliest attacker David Connelly should have done better with a free header, but his weak effort was easily saved by Alan Combe.
Pardew sent on Zamora as a second-half substitute and a series of corners spelled danger for the Bantams.
Just after the hour, the pressure finally told when Combe flapped at a hit-and-hope cross and when Hammers skipper Christian Dailly hooked the ball back across goal Zamora nodded home from six yards out.
City's hopes of hanging on for a point were dashed 12 minutes from time when Connolly's neat flick put Harewood clear and the Hammers hotshot drilled a ten-yard drive through Combe's legs.
Armstrong finally found the net eight minutes from time, but his scrambled effort was ruled out for offside.