Redhill boss Ian Dawes rated Horsham YMCA "probably the best side we have played all season" after a 2-0 defeat at Gorings Mead.
Paul Young twice volleyed against the woodwork and also hit YM's clincher.
Nick Flint was the provider, having also been involved in a ferocious finish by Joel O'Hara to open the scoring.
Horsham stay second, nine points behind the leaders having played two games more.
Meanwhile, Sidley came from a goal down for a routine 2-1 success at Littlehampton.
Kevin Rose hit a quick equaliser and Wes Tate forced the own goal which settled matters.
Three Bridges enjoyed a second successive victory as they beat Ringmer 3-1 thanks to late goals from Seb Favata and Phil Gault.
Pat Massaro had given Bridges an early lead with a great individual goal but Warren Byerley replied with a header just before half time and it looked like staying that way until the closing stages.
Favata then put Bridges back ahead with a wonderful overhead kick and Gault wrapped things up with his 20th of the season.
Relegated Wick beat Arundel 3-1.
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