First-half goals by Kevin Davies and on-loan Jack Wilshere sent the visitors on their way to three points and, even though the Trotters saw Tamir Cohen dismissed and Alessandro Diamanti net a late consolation, those early strikes still proved sufficient to send them leapfrogging over the Hammers.
West Ham may have kicked off in the heady heights of 13th spot but they were still only one point and two places ahead of Bolton in the congested drop zone.
And while Gianfranco Zola's England trio of Carlton Cole, Robert Green and Matthew Upson had returned from international duty unscathed, the same could not be said for Owen Coyle, who was forced to make one change from the side that had beaten Wolves last weekend as Cohen came in for Stuart Holden, who broke his leg in the USA's friendly defeat against Holland.
But they still had the talismanic Davies, who got between James Tomkins and Julien Faubert to powerfully nod his side ahead on 10 minutes after Gretar Steinsson invited the overlapping Chung-Yong Lee to send the perfect, pinpoint cross towards his skipper on the edge of the six-yard box.
Having just notched his sixth goal of the season, the Trotters captain then tormented Tomkins again when he stopped the hapless Hammers defender from shepherding the ball out of play before whipping a centre towards the penalty spot, where Cohen headed into the path of Wilshere, who crashed home his first goal for Wanderers since joining them on loan from Arsenal.
With just 15 minutes on the clock, the East Enders were in meltdown and it could have got even worse as Johan Elmander forced Green into a crucial low save, before unleashing another effort into the side-netting.
On 25 minutes, however, Paul Robinson was booked for felling the fleeing Valon Behrami and Diamanti saw his consequent free-kick clawed away by the flying Finn and, as the break neared, Parker released Cole, who was brilliantly robbed by Sam Ricketts as he shaped to shoot.
Right on half-time, Zat Knight was forced to hook off the line after Diamanti's cross deflected off Robinson, while at the other end the unmarked Elmander wastefully fired skywards in stoppage-time from just six yards.
Within seconds of the restart, a hamstring injury to Faubert resulted in Kieron Dyer stepping from the bench and the Hammers substitute wasted no time sliding over from ten yards.
On the hour, Diamanti drilled wide from long range and, after both Fabrice Muamba and Cohen were cautioned for feisty challenges on Parker and Behrami, Zola brought on Mido for Guillermo Franco, whose last act of a miserable afternoon had seen him scuff over.
And with 20 minutes remaining, another clumsy Cohen challenge saw the Israeli midfielder pick up his second yellow card of the afternoon to put unnecessary pressure on his side.
Sure enough, Diamanti's wonderful 18-yard curler gave Hammers just a sliver of hope with just two minutes left but, after the breaking Davies slid Knight's cross onto the angle, the woodwork came to the rescue of the ten men, when substitute Junior Stanislas rocked the crossbar with an 18-yarder in stoppage time.