Manager Steven King believes lack of concentration could cost Lewes the division one south title.
Rooks conceded a last-minute goal and lost 5-4 at Leatherhead to remain in second place, two points behind leaders Windsor and Eton.
Lewes were trailing 4-1 in the first half after two goals apiece from Phil Ruggles and Paul Hartford.
Lewes' goal came from Warren Haughton, who went on to claim a hat-trick with two more either side of half time.
The visitors thought they had snatched a point when Jay Lovett equalised with a header from a Dwain Clarke corner, but Ruggles won it for Leatherhead in the dying stages.
King said: "We can't seem to stay switched on when it matters.
"Lapses in concentration have been costing us a lot of games recently and the players don't seem to learn from it."
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