Hailsham were promoted from Rich City County League division two on Friday night following a goalless draw at East Grinstead.
In a game where defences were on top throughout, Hailsham almost snatched victory late on when Steve March hit the foot of a post with a header.
Hailsham boss Mark Leaney said: "I thought we might be in contention at the start of the season, maybe top five.
"We have a young an inexperienced side but maybe we have proved a few people wrong.
"At the end of the day we have just done enough."
The result all but ends East Grinstead's own promotion push. They need to win their remaining three matches and hope that Peacehaven lost both of their remaining games.
In division one, Redhill won 2-1 away to Horsham YMCA thanks to a brace from Matt Kelly.
The striker opened the scoring in the third minute and added a second on 17 minutes. Lee Butcher scored a consolation for the hosts five minutes from time.
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