A first-half penalty from Ryan Walton and Ian Robinson's effort in the second 45 minutes ensured Newhaven ran out 2-1 winners at Culver Road.
After going a goal down inside ten minutes, Lewis Finney's clever shot on the spin hauled Lancers level three minutes before the break.
Having worked so hard to get back in it, Ian Robinson struck the winner two minutes after the restart to seal all three points for Dockers.
A difficult day for Lancing was then rounded off with a red card 20 minutes from time. Following a reckless lunge from Jake Chadwick on Ian Robinson, the former was sent for an early bath.
After a quiet opening ten minutes, Dockers were gifted the chance to go in front. Ryan Walton took a Lee Robinson in his path, before going down under a challenge from Lancers goalkeeper Tyler D'Cruz in the area with a spot-kick awarded. Walton then dusted himself down and fired home the penalty.
Lancers responded well to going behind, with Finney twice denied by Jake Buss in Newhaven's goal, prior to levelling on 42 minutes.
Finney cleverly spun and struck an effort past Buss into the bottom corner to make it 1-1.
The winning goal then came two minutes into the second period. D'Cruz could only parry Lee Robinson's effort straight into the path of Ian Robinson, who was on hand to slot home.
Lancers were then reduced to ten-men 20 minutes from time as Chadwick's late lunge on Ian Robinson saw him shown a straight red with frustrations boiling over.
Lancing travel to Loxwood in the league on Saturday.
LANCING: D'Cruz; E.Finney, Sharman, Berry, Fenton; Waterman, Williamson, Caplin; Chadwick, L.Finney, Bennett. Subs: Dramir (Bennett, 60), Walsh (Caplin, 73), Baah (Waterman, 88), Donaldson, Fidler.
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