Selsey were unable to hang on for three points as ten-man Sidley scored a late equaliser to salvage a 1-1 draw at the High Street Ground in division one of the Sussex League.
The hosts took the lead just after half-time and Sidley goalkeeper Josh Willis was sent off for a professional foul on the hour.
But with less than ten minutes to go Lewis Hole was judged to have been brought down in the area and Casey Ham stepped up to rescue a point.
Despite the late disappointment, this left Selsey unbeaten in four matches and 14th in division one.
But that run without any defeats ended on Tuesday when they lost 2-0 at Worthing United.
The loss ruined a run in which a series of stoic defensive showings had seen Selsey concede just three goals in four games since the 6-1 defeat to Burgess Hill last month.
But with games in hand over nearby teams and triker Robert Wimble in hot form, Selsey can aim to push up the table in the run-up to Christmas. They host Redhill at The High Street Ground on Saturday.