The 2-1 home win keeps the Hornets in fourth, but moves them level on points with place-above Enfield Town going into Tuesday’s game at old foes Lewes.
The U’s, meanwhile, drop to ninth and are now six points adrift of the play-offs.
Horsham opened the scoring from the penalty spot on 12 minutes. Danny Barker was brought down in the box and James Hammond duly dispatched the spot kick.
And the Hornets doubled their advantage 14 minutes later. An excellent piece of pressing from Dan Ajakaiye on Hastings keeper Charlie Grainger saw the Horsham striker tackle the former England under-18 international and fire home.
The U’s reduced the arrears on the hour mark. Sam Cruttwell squeezed the ball past Hornets stopper Lewis Carey to give the visitors hope, but the hosts held on to claim the three points.
Both sides are in action over the Easter weekend. The U’s travel to third-from-bottom Haringey Borough on Good Friday, before entertaining Folkestone Invicta on Easter Monday.
Horsham, meanwhile, visit Cheshunt this Saturday and host West Sussex neighbours Bognor Regis Town on Easter Monday.
See some of John Lines’ pictures from the game on this page and the ones linked. You can read Horsham manager Dominic Di Paola’s thoughts in the West Sussex County Times, out every Thursday, and Hastings United boss Chris Agutter’s views in the Hastings Observer, which hits the shelves every Friday.
1. Horsham FC boost play-off hopes with Sussex derby victory over Hastings - the match in pictures
Action from Horsham v Hastings Photo: John Lines
2. Horsham FC boost play-off hopes with Sussex derby victory over Hastings - the match in pictures
Action from Horsham v Hastings Photo: John Lines
3. Horsham FC boost play-off hopes with Sussex derby victory over Hastings - the match in pictures
Action from Horsham v Hastings Photo: John Lines
4. Horsham FC boost play-off hopes with Sussex derby victory over Hastings - the match in pictures
Action from Horsham v Hastings Photo: John Lines