Albion had won six on the spin against the Hammers in the WSL but Kirsty Smith’s early goal and Riko Ueki’s second-half header proved the difference at Broadfield Stadium on Sunday.
Elisabeth Terland and Pauline Bremer went closest for the hosts but West Ham came away with the victory to leave Melissa Philips’ side with three points from their opening two league matches.
The visitors nearly took the lead inside the first minute as the hosts failed to clear Lisa Evans' cross into the six-yard box but Kirsty Smith couldn't keep her shot under the bar.
West Ham then went ahead just over 10 minutes later as although goalkeeper Sophie Baggaley did superbly to tip Riko Ueki’s long-range strike, she was unable to keep Smith’s follow-up from creeping over the line.
Elisabeth Terland, who scored both of Albion’s goals in a 2-1 win at Everton last weekend, nearly equalised shortly after as her powerful drive from just inside the area was expertly saved by a diving Mackenzie Arnold.
While Rehanne Skinner’s team looked a threat throughout, it was Brighton who nearly levelled the scores late on in the first half.
First, Pauline Bremer’s powerful shot from inside the box was parried by Arnold, before Terland looped her strike just over the crossbar. And then Terland flashed a shot just wide of the past in first-half stoppage time after good work from Geum-Min Lee.
Albion’s hopes of a second-half comeback were dealt a huge blow when Evans’ free-kick was nodded home by Ueki and it was nearly 3-0 when West Ham’s number nine brought a good, reaction save out of Baggaley.
Albion rang the changes in the final 35 minutes but the Hammers, who went close again late on through the dangerous Ueki, kept them at arm’s length.
Substitute Madison Haley, who made her Albion debut, looked bright in the game’s dying embers, but in the end West Ham deservedly claimed the three points after 10 minutes of second-half stoppage time.
Phillips’ team are in FA WSL Cup action on Wednesday when they travel to Championship side Birmingham City.
Albion: Baggaley, Thorisdottir, Pattinson (Rule 57), Bergsvand, Losada (Symonds 66), Bremer (Pinto 66), Lee (Haley 57), Zigiotti, Terland, Kullberg (Sarri 81), Robinson.
Subs not used: Evrard, Carabali, Hawkesby, Startup.