Horsham suffered a second-half collapse as promotion chasing Dartfordians ran in six tries after the break for a comprehensive 53-17 victory at Hammerpond Road.
The result moved the visitors up to third in the table, level on 60 points with Old Colfeians, while Horsham remain sixth.
Horsham started well and took an early lead with tries from Richard Tredgett and Rob Grant, but Dartfordians came back strongly scoring seven tries before Josh Steggles added a consolation try in the final minute.
After just six minutes, good pressure from Horsham’s attacking play led to a lineout in the corner after which Tredgett scored from a well-worked move and Will Bell added the extras for a 7-0 lead.
Dartfordians then scored out wide through Ollie Edwards following several phases of quick ball.
The Green and Whites bounced back after 21 minutes with some fine multiple phase play after which the ball was released for Grant to score in the corner to take a 12-5 lead.
Horsham continued to attack the Dartfordians try line but found it difficult to break down a resolute defence, while the visitors pulled the score back to 12-8 with a penalty.
A quickly-taken tap penalty then saw Sam Cooksley go over and Mike Briggs convert to give Dartfordians a 15-12 lead into half-time after a well-contested first half.
Darts looked sharper in the second half and Grant picked up a yellow card, but while the Green and Whites tried to stem the tide, the visitors showed they were in a ruthless mood.
They scored six second-half tries through a Connor Sutherland hat-trick, Ryan Chandler brace and one for Simon Briggs as they opened up the Horsham defence, before Steggles scored his consolation following some multiple phase play.
Holders Horsham are in action in a home Bob Rogers Cup clash this weekend against Chichester 2nds.
Horsham: Brady, Grantham-Hill, Barber, Goward, Tredgett, O’Rahilly, N.Bell, Whiting, Steggles, W.Bell, Crook, Carvell, J.Bell, Grant, Nwachukwu. Subs: Clarkson, Maguire, Jenkins.