Just three minutes into the game, Charlie Hester-Cook burst into the 18-yard box and took aim at goal in the first Horsham chance of the game, with his drive being spilt by goalkeeper Toby Bull into the net.
The real turning point in the game came in the 70th minute, when the Rooks’ Peter Ojemen was shown a straight red card for a mistimed tackle on Chris Dickson.
Horsham secured the win on 78 minutes. Dickson drove a shot at goal from distance, and after being charged down the ball fell to James Hammond, who easily converted from six yards.
Lewes now sit third in the Isthmian Premier, having started the day at the summit, while the Hornets move up to eighth.
You can read Will Hugall's full match report here.
See some of John Lines’ pictures from the game on this page and the ones linked.
1. Horsham FC topple old foes Lewes FC to claim Sussex derby bragging rights - the match in pictures
Action from Horsham v Lewes Photo: John Lines
2. Horsham FC topple old foes Lewes FC to claim Sussex derby bragging rights - the match in pictures
Action from Horsham v Lewes Photo: John Lines
3. Horsham FC topple old foes Lewes FC to claim Sussex derby bragging rights - the match in pictures
Action from Horsham v Lewes Photo: John Lines
4. Horsham FC topple old foes Lewes FC to claim Sussex derby bragging rights - the match in pictures
Action from Horsham v Lewes Photo: John Lines