Oak jump to second place
Oak moved above Rustington and Lingfield, whose matches were postponed owing to waterlogged pitches.
Steve Porter, Danny Curd and Keiron Howard, with two, were on target for Oak who led 4-0 before Heath scored a late consolation.
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Hide AdOak are now two points clear of both Rustington and Lingfield but have played three games more.
Southwick are now safe from relegation after their 3-1 win at Crawley Down. They came from behind to win with goals from Jack Hayward, Danny Molineaux and John Elliott.
For full match reports, see the April 3 edition of the Shoreham Herald.