The Rocks slipped out of the cup after a ‘sterile’ display in the final third saw them fire another home blank against arch rivals Whitehawk.
They matched the premier division leaders for much of the game and had plenty of possession, but once again lacked the killer touch where it mattered.
Darin Killpartrick praised the players for their effort but said the Rocks needed a fully-fit Ashley-Paul Robinson/Terry Dodd partnership again to start finishing off opponents.
Charlie Walker scored the only goal midway through the second half of a fairly forgettable game and the Rocks had no reply.
Killpartrick said: “We did okay - it was a competitive game but I’d describe our play in the final third as sterile.
“We were spoiled with Jason Prior knocking in goals every week and we have to realise goals won’t come without effort and sharpness in the box.
“Ashley-Paul is not fully fit after his injury and Terry has problems with his shins again, but if we could get those two 100 per cent ready and playing together in a run of games, I’m certain the goals would flow.
“Without them firing on all cylinders, it’s difficult.”
The first attack of the night saw Robinson cross from the left but Steve Harper’s glancing header was comfortably saved.
For Whitehawk, Ramone McCrae played in Josh Jones but from a tight angle he chipped wide of the far post.
Tom Boyle had to come out of his goal mouth to gather an awkward bouncing cross from ex-Rock Mark Knee.
Jon Marzetti received a yellow card for a late sliding challenge on Knee on a slippery surface.
Harvey Whyte and Dan Beck combined well for the best passing move of the game but it came to nothing.
Robinson was replaced by Carl Walshe for the second half and Dan Sackman and Ollie Pearce replaced Stuart Axten and Harper soon after the break.
The Hawks scored when a lofted ball forward found Charlie Walker and after outpacing the defence he slotted low into the net from just inside the area.
Walshe waltzed his way across the defence before striking with a low with his left boot – forcing Winterton into a fine diving save. At the other end Boyle saved from Mills.
Ex-Rock James Fraser came on for Whitehawk to boos from the Nyewood Lane faithful.
A cross from Jones led to disarray in the Bognor box as Sackman almost scored in his own net. Luckily Boyle was there to block that as well as a follow up attempt by a sliding Fraser.
Whyte swivelled past Jones before getting to the area and flashing a left footed driven shot well wide.
Rocks: Boyle, Marzetti, Beck, Stockford, Axten (Sackman 52), John, Whyte, Wills ©, Harper (Pearce 57), Robinson (Walshe HT), Tuck. Unused subs: Crane, Cody.
LIAM GOODLEY & STEVE BONE