Grant Holt's double maintained Forest's 100% start as the striker ended his side's jinx of having missed penalties in their three previous league games.
Holt opened his account for the season with a brace
Forest had to come from behind after Alex Revell crossed for Jake Robinson to fire home in the first half.
Holt fired Forest level from the spot just before the hour mark after Jack Lester was fouled by Adam El-Abd.
Holt then headed past Wayne Henderson before El-Abd was sent off in the final minute following a second yellow card.
Nottm Forest: Smith, Morgan (Curtis 45), Breckin, Cullip, Southall, Perch (Thompson 84), Gary Holt, Clingan, Bennett, Grant Holt, Lester (Harris 70).
Subs Not Used: Pedersen, Weir-Daley.
Goals: Grant Holt 63 pen, 78.
Brighton: Henderson, Reid (Santos 90), Lynch, El-Abd, Mayo, Hammond, Carpenter, Stokes (Frutos 73), Revell, Hart, Robinson (Cox 54).
Subs Not Used: Kuipers, Lowe.
Sent Off: El-Abd (90).
Booked: Mayo, El-Abd.
Goals: Robinson 39.
Ref: M Clattenburg (Co Durham).