O'Sullivan said his side was approaching the contest in a carefree manner.
"We're stoked, it's a great opportunity. They're the favourites so we have nothing to lose."
The concerns come are in defence where injuries - especially at the troublesome right back position - have led to major reshuffling.
"We've been conceding a few soft ones lately, and seem to get run down in the last 20 minutes. It seems like right back is a bit of a cursed position."
The side is the only WaiBOP Federation One club remaining in the Chatham Cup following high scoring shoot-outs in the first two rounds.
An opening 4-3 win in Pukekohe was followed by a 4-2 victory over the South Auckland Rangers, leaving Ngongotaha AFC as one of the lowest ranked sides of the 32 left in the draw.
The match is one of 10 Chatham Cup matches being played on Saturday, following Western Springs AFC and Bay Olympic kicking off the round tomorrow night.