Hailsham Town and Selsey secured their first division survival on a day when Peacehaven took a step closer to second division football.
A 3-0 win for Hailsham at home to Peacehaven means the hosts cannot be relegated.
Selsey's 5-0 win at home to Shoreham kept them up and it means Peacehaven will be the third team relegated this year if Arundel get at least one win from their remaining nine games.
Hailsham boss Brian Dennis said: "It was probably the most important game of the season because of the position we had got ourselves in.
"It was a good performance. It could have been a few more but I will take 3-0."
Leon Legge opened the scoring with a header from Ross Southwood's free kick and Southwood added a second himself before half time when he snapped up a rebound after Damien Smith's shot had been parried.
Scott French wrapped up victory with a smart finish in the closing stages.
Selsey sunk Shoreham with second half goals from Clinton More (2), Paul Lee, Matt Stillman and Jason Reed.
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