The home side took the lead through Ollie Morgan jjust after the half-hour mark and Horsham keeper Lewis Carey was in superb form to stop them increasing the lead.
Harry Hedges scored his first senior goal for the Hornets in the last minute of normal time, but Salisbury still had time to find a winner - through ex-Worthing striker Nathan Odokonyero – in the final minute of added time.
The defeat leaves Horsham 15th and with one game to play, they can finish no lower in their first season at step two. They round off the campaign at home to Chippenham next Saturday.
See pictures from Salisbury 2 Horsham 1 by McCartney Martin on this page and those linked. Get the Hornets latest in the West Sussex County Times, out Thursday.
61. Salisbury v Horsham pictures by McCartney Martin (97).jpg
Salisbury v Horsham, National League South Photo: McCartney Martin