PORT edged out a spirited Prenton side in what was always going to be a difficult encounter for a place in the semi-finals of the Cheshire Plate.
Port dominated the early stages but again failed to take their chances, and it was the home side who struck first blood with two unconverted tries ran in from their own 22, very much against the run of play.
Prenton's lead could have been increased but for a try-saving tackle from full-back Chris Byrne and an excellent rob on the Port try-line by Dick King. On the stoke of half-time, Don Charvis put Port back in contention with a typical winger's try, duly converted by captain Steve Foster to reduce the deficit to 10-7.
The second half began in the same vein as the first half, but this time Port took their chance as makeshift centre Nathan Mullet-Jones carved his way through the home defence for an unconverted try.
A Prenton penalty put the home side back in front but, coolness personified, Foster slotted a late penalty to put Port deservedly into the semi-finals.
Man-of-the-match was Steve Foster. Port seconds gained an excellent victory against a vibrant Birkenhead Park XV, packed with university backs whose interplay bemused Port early on and led to a 10-0 lead for the visitors.
As the game wore on, Port's pack began to dominate as seasonal debutants John Doom and Dan Schu took control. The visitors could not contain the power and pace of the back row as number eight John Doom went over unchallenged and veteran winger Ian Sconson ran the length to score.
The glory was left to ever-present Chris Evans to kick the winning penalty from the touchline to secure a 13-10 victory.