Kieron St Aimie headed home a Sam Collins cross for the only goal of the Ryman Football League Premier Division clash in the 89th minute.
The goal came just 15 minutes after the usually clinical Sam Adams had seen a penalty saved by the Hornchurch goalkeeper following a foul on Kenny Pogue.
United were without Harry Beautyman, Ben Davisson, Matt Hall, Scott Manning, Tim Olorunda and Ross Sutton, and were only able to name one outfield substitute.
Ben Billings and Sam White made their full debuts on either side of midfield, while Pogue made his first start since early November. Youth team striker Mark West made his league debut as a late substitute.
United (4-4-2): Barton; Rowe, Ray, Jirbandey, Storrie; White, Eldridge, Adams, Billings; Porter, Pogue (West 86). Sub not used: Chalmers-Stevens.
A full report will appear in Friday’s Hastings Observer.
United remain in the final safe spot of fifth-from-bottom after fourth-bottom Aveley lost 2-1 at Canvey Island. Croydon Athletic won the battle of the bottom two away to Maidstone United by a goal to nil.
Bottom six (played-points): Horsham 34-32, HASTINGS UNITED 33-29, Aveley 32-26, Folkestone Invicta 32-25, Croydon Athletic 33-25, Maidstone United 33-21.
LAST NIGHT’S OTHER RESULTS
Sussex County League, John O’Hara League Cup semi-final: Rustington 1 RYE UNITED 2 (at Peacehaven & Telscombe FC).
Hastings & District FA Senior Cup semi-final: BEXHILL UNITED 2 LITTLE COMMON 1.
More to follow.