Steve Burton's first-half strike gave Crawley victory in a scrappy contest.
Burton neatly turned in Tony Scully's cross from six yards seven minutes before the break to give Crawley a deserved win.
Forest Green almost levelled seconds after the restart but Julian Alsop's header was well saved by home goalkeeper Phil Smith.
But Crawley had the better chances and Paul Armstrong should have doubled the lead but volleyed wide from 18 yards.
Crawley Town: Smith, Judge, Mendy, Giles, Brown, Clay, Armstrong, Blackburn (Jenkins 63), Scully (Bostwick 89), Coleman, Burton.
Subs Not Used: Ward, Ekoku, Woozley.
Booked: Brown, Mendy.
Goals: Burton 38. Forest Green: Clarke, Simpson, Michael Taylor, Sall, Jones, Searle, Meechan, Beesley (Dove 65), Brough (Teixeira 83), Madjo, Alsop (Abbey 76).
Subs Not Used: Graham, Harrison.
Booked: Simpson, Jones.
Ref: R Lee (Essex).