Crawley blew a huge hole in Bognor's title plans but a Sussex promotion double from London Four South East is looking increasingly likely.
A 17-10 win by Crawley at Hampshire Avenue, coupled with leaders Chichester beating Bromley 17-3, means Chi and Bognor look like going up.
Crawley, though, have not given up hope and have still to play Chichester at Willoughby Fields.
Lee Preston's chip-and-chase and strong finishes from forwards Simon Matterface and Luke Denham clinched an impressive win at Bognor, with Andy Evans adding a conversion.
Tom Spurle and Paul Mitchell scored Bognor's tries but skipper Karl Flynn admitted: "We are putting pressure on ourselves. I am disappointed in everybody."
Promotion looks a formality for Chichester after scores from Simon Bradford and Richard Johnson, plus a penalty try, clinched the 17-3 home win over Bromley.
Nick Stanton added a conversion for Chi, whose win did Bognor a big favour.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article