Green and Whites head coach Nick Stocker felt it was a lethargic showing from his side in a match they could have won.
He said: "It was one of those games where we didn't get out of second gear. It was a disappointing result as we certainly had the capacity to win. They are a tough team to beat away from home and it was a frustrating day on the field."
The game started in chaotic fashion with Jonny Whiting receiving an early yellow card for a late tackle. However Horsham didn't let this deter them when moments later Joe Wilde was sent under the posts after a delayed pass from Tom Johnson which Johnson also converted.
From a free kick at the scrum the Green and Whites increased their lead when the ball was tapped quickly and spun wide for George Palmer to finish in the corner and Horsham lead 12-0 after 19 minutes.
The lead rather flattered the visitors as Deal & Betteshanger were making numerous handling errors, missed a couple of kicks at goal, and even managed to lose control of the ball when over the line in the act of scoring, but eventually scored a good try after multiple phases close to the breakdown, to narrow the deficit as Horsham took a 12-7 lead into the break.
Deal & Betteshanger levelled the scores early in the second half from a turnover at the scrum and their winger raced in to score to set up a nail-biting final climax.
Horsham thought they had won the game with an unconverted try from Canice Gonzague following good first phase attacking play before a converted try for the hosts saw them secure a last gasp win.
There's plenty for Horsham to be excited about with nine members of the side being under 23 giving real hope for the future with Stocker adding: "With a lot of young players coming through you start to see the potential of the team and we want to progress and start challenging for honours."