Selsey were punished for another lacklustre first-half display at Glovers Lane as Sidley United ran out 4-0 winners in division one of the Sussex League.
The visitors were two goals behind after just 11 minutes, Brett Patten and Jared Lusted striking early on for Sidley.
Lewis Hole headed home five minutes before the break to make it another first period where Selsey were much the inferior team this season.
Despite going down to ten men late in the second half having used all three substitutes when a player went off injured, Sidley found time for another goal with Jason Taylor adding the fourth in the dying minutes.
Selsey boss Adam Hinshelwood will be concerned at the nature of the defeat and in particular at the number of goals conceded - now 11 in their past three.
Three points for Sidley lifts them into the top half of the table, six points ahead of Selsey, who have lost the advantage of games in hand on some of the teams around them.
Unable to capitalise on a poor result for Crowborough, Selsey now gear up for the visit of East Grinstead Town on Saturday knowing a win would bring them to within two points of their opponents.