Lewes have now gone seven games without a win after losing 2-0 at home to lowly Banstead Athletic.
The Rooks have now been leapfrogged by Horsham and find themselves out of the top three, but know they can still reignite their promotion charge if they win their games in hand.
The Rooks got off to the worst possible start as they fell behind on two minutes when a huge throw from Wayne Finnie was not cleared and James Greenaway pounced on the loose ball to score past Russell Tanner.
On 25 minutes a 30-yard free kick from Banstead's Barry Langford flicked off the top of the Lewes crossbar.
The Rooks had only created a couple of half chances for Julian Curnow and Danny Davis until six minutes from the interval when Matt Allen headed over Banstead goalkeeper Paul Borg but his effort was hooked off the line by Aaron Day.
A minute into the second period Banstead's Mark Leahy repeated the feat when he headed Justin Harris' goalbound looping shot away from under his own crossbar.
Banstead's second came courtesy of a dreadful error by Tanner who allowed Michael Beale's tame shot to go through his hands and legs.
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