Crawley Down Gatwick put Hassocks onto the backfoot for most of the first half but frustratingly were unable to produce the goods when they needed to.
Hassocks took the lead after 12 minutes when Phil Johnson seized on a pass to cut inside and fire past keeper Andy Greaves to give the visitors first blood.
It took the Anvils until the 20th to make the first real effort on the Robins goal when a jinking run by Jeff Mahadoo found a gap to fire at keeper George Willett who turned the shot away.
Sam Cane’s off-target shot was Down’s only other chance before half-time.
Hasocks made it 2-0 on 50 minutes when flankman Jamie Hillwood now on the right took a long ball out of defence cut inside to score off the far post.
The Anvils fought back just two minutes later when Lee Thomas blasting home from well outside the box to narrow the deficit to a single goal.
Down went closer to equalising in the 70th minute when Grant Rigler setting up Leyton Regan whose crossfield shot just screwed past the far post.
Despite more Down pressure, Hassocks hung on to claim the three points.
Down finished the game with just ten men as Josh Alcott received a straight red card ten minutes before the end for a rash lunge.
Crawley Down Gatwick: Greaves, Cooney, Lovett, Goodwin, Dormoraud, Reid, Alcock, Cane, Regan, Mahadoo, Thomas (Rigler). Subs: Steers, Mutungi
Man of the Match: Leyton Regan