Despite going behind to an early strike from Chris Andrews, the Easterners crossed over leading 3-1 before adding a fourth goal ten minutes from the end.
Luke Watson levelled matters after 15 minutes and then two goals in quick succession shortly before the break, from Matt Rawlings and a St Brelade defender, put St Clement in control.
Martin Godfray completed the scoring late on to set up a re-run of last year’s final, tomorrow, at St Saviour, kick-off 1.30 pm.
St Clement manager Ken Addison said: ‘It was relatively comfortable in the end, but we had a poor start and only played well for 20 minutes in the first half after going behind.
‘I think the lads thought it was going to be a bit of a stroll at the time but it certainly wasn’t.
‘Our passing was awful at times, we gave the ball away so much but it was much better after the break when Luke Watson and Jerry O’Shea played well in midfield while Stuart Andr? was outstanding in defence.’
St Brelade player-manager Darren Mollet said: ‘It was good game, both sides attempted to keep the ball on the ground and it was end-to-end throughout.
‘Our marking was lapse for their first and second goals and then I stretched to block a cross and unfortunately I poked the ball into our goal for their third.
‘Their fourth goal we thought was well offside but the assistant did not raise his flag.’
Andrews’ opener for St Brelade was a fine goal, the Island player beating two players following a run from the half-way line before despatching the ball into the goalkeeper’s bottom right-hand corner from the edge of a penalty area.
St Clement or St Saviour will play St Ouen in a semi-final at Les Quennevais next Wednesday while the other semi is tomorrow with St Peter hosting, kick-off 1.30 pm.