The German scored Brighton’s first top-flight goal since 1983, latching on to Solly March’s cross at the far post in the last action of the first half.
Gross sparked more jubilant scenes when his 25-yard effort flew past Ben Foster on 48 minutes.
The 26-year-old summer signing soon turned provider to enable Tomer Hemed to head in a third.
A close-range James Morrison strike could not spark a comeback from Tony Pulis’s side, who drop to eighth.
Brighton climb to 13th with four points from as many matches.