Brighton scored two goals from two shots on target to maintain their unbeaten start to the season with victory at West Ham, who remain without a league goal or a point.
Alexis Mac Allister scored the opener from the penalty spot after West Ham summer signing Thilo Kehrer brought down Danny Welbeck just inside the area on his Premier League debut.
The Hammers started the second half brightly but were undone when Leandro Trossard latched on to Pascal Gross's flick to inflict a third straight league defeat on the hosts.
Afterwards, Hammers boss David Moyes said he was "concerned" by his side's start to the campaign.