Horsham reached the FA Cup second round for the first time in their 136-year history largely thanks to a Lee Carney double that helped see off Maidenhead.
Nigel Brake gave the Sussex side the lead with a tremendous 35-yard effort before Carney added the second.
Dwane Lee pulled one back from the spot for the visitors after Kevin Hemsley hauled down Manny Williams.
Carney made it 3-1 that led to Gary Charman's red card for over celebrating before Lee Farrell grabbed the fourth.
Horsham: Mansfield, Myall, Brake, Graves, Hemsley, Carney, Mingle, Taylor, Austin (Farrell 78), Rook, Charman.
Subs Not Used: French, Westcott, Salaam, Seuke.
Sent Off: Charman (85).
Booked: Austin, Charman, Mansfield, Taylor.
Goals: Brake 45, Carney 62, 83, Farrell 90.
Maidenhead Utd: Wells, Sterling, Smith (Newman 80), Nisbet, Clarke, Lee, Daly, Brown, Benjamin (Makofo 74), Williams, Yashwa (James 69).
Subs Not Used: Cooper, Ramos.
Goals: Lee 64 pen.
Ref: A Halliday (West Yorkshire).