Charlie Hester-Cook fired home from close-range to give the Hornets a half-time lead.
Louis Britton levelled for the Seagulls four minutes into the second half before Jason Pope was given his march orders on 75 minutes after hauling down Horsham’s Ricky Aguiar.
The Hornets are now fifth in the National League South, four points adrift of new leaders Torquay United having played a game more.
Horsham travel to bottom-of-the-table Chippenham Town this Saturday.
1. Horsham FC extend unbeaten run with draw against ten-man Weston-super-Mare - the match in pictures
Horsham FC extended their unbeaten run to 15 games in all competitions with a 1-1 home draw against ten-man Weston-super-Mare in the National League South. Photo: John Lines
2. Horsham FC extend unbeaten run with draw against ten-man Weston-super-Mare - the match in pictures
Horsham FC extended their unbeaten run to 15 games in all competitions with a 1-1 home draw against ten-man Weston-super-Mare in the National League South. Photo: John Lines
3. Horsham FC extend unbeaten run with draw against ten-man Weston-super-Mare - the match in pictures
Horsham FC extended their unbeaten run to 15 games in all competitions with a 1-1 home draw against ten-man Weston-super-Mare in the National League South. Photo: John Lines
4. Horsham FC extend unbeaten run with draw against ten-man Weston-super-Mare - the match in pictures
Horsham FC extended their unbeaten run to 15 games in all competitions with a 1-1 home draw against ten-man Weston-super-Mare in the National League South. Photo: John Lines