Barnham were below-par as they allowed promotion rivals Forest to leave Mill Road with a 3-1 win in division three of the Sussex League.
The Trojans had a few players carrying slight knocks and after a frantic start, Barnham took the lead through striker Ash Harper as he coolly rounded the Forest keeper and stroked home from eight yards.
Forest replied instantly with Shaun Findley curling an effort round the hapless Byron Kearns from just outside the area.
The rest of the half saw Forest dominate possession but without creating any concrete chances.
Barnham started the second half brightly with several half-chances created in the first ten minutes.
But Forest struck again from the penalty spot after Perry Northeast was adjudged to have brought down Joe Holvey in the area, a harsh but fair decision.
Holvey stepped up to take the penalty and made no mistake.
Minutes later midfielder Paul White ensured Forest went home with three points with a tidy finish after great footwork inside the Barnham half.
The last few minutes saw Barnham try to salvage something but it was too little too late.
It was a disappointing performance from a Trojans side who had felt confident of three points.
BARNHAM: Kearns, Wood, Walters, Johnson, Newman, Noble, Northeast, Boxell, Hancock, Enticott, Harper. Subs: Hibbert, Pedrick, Salisbury.