Pembrokeshire were soon behind in this return game with Carmarthenshire, and found the pace hard to find as the visitors attacked dangerously down the right.
A ground shot found the net, and the home team could not find the rhythm to get Ashley Bevan and Jay Brockway clear of the visitors to level matters up.
Carmarthen did not add to their lead until just on half-time, but the 2-0 scoreline fairly reflected their edge in the match.
Pembrokeshire started well in the second half, producing good passing movements, and a more positive attitude to scoring.
From a fine free-kick taken on the left by Brockway, Bevan headed in from six yards to put the home team back in the game.
With this encouragement, Pembrokeshire played the ball around well, with Joey Jones and Stephen Pugh supplying their strikers with good passes before they were dispossessed by the visitors' goalkeeper.
As Carmarthenshire got back in the game, they scored a headed goal from a corner, with Liam James diving far to his left and being just unable to keep the ball out of the net.
Despite a good all round effort, Pembrokeshire could not get the goal needed to improve the scoreline and push for an equaliser.
Although losing 3-1, Pembrokeshire still progress to the quarter-final of the Welsh Schools' competition where they will again meet Carmarthen in what promises to be an exciting encounter.
Thanks are due to Tenby AFC for the use of their facilities.
Pembs. squad: Jason Clarke, Jordan Harding, Ashley Bevan (Milford), Daniel Richards, Joey Jones, Greg Brown, Stephen Pugh, Tom Glover, Stephen Dockerty (STP), Steffan James (Preseli), Jay Brockway, Liam James, Steven Mills (Taskers), Rhys Darling, Gary Delaney (Fishguard).