
The Seagulls continued their perfect start to the season with a 2-0 victory at West Ham, who remain without a point.
Danny Welbeck was brought down by West Ham summer signing Thilo Kehrer just inside the area for the first goal of the season.
The Hammers started the second half brightly but were undone when Trossard latched on to Gross's flick to seal a third straight league defeat.
Robertnchez produced two acrobatic saves late in the game to keep out two Tomas Soucek crosses.
West Ham have had 38 shots in their first three league games without scoring a goal, which is why they lost to the Seagulls.
The Hammers are at the foot of the table after losing their first three games of the season, while the Seagulls moved up to fourth.
