Portobello started the stronger side and took the lead in the seventh minute, Kieran Wilson playing in Alfie Smith to guide the ball into the back of the net.
Porty took a 2-0 lead when Owen Hastie battered a shot at goal and the ball took an unlucky deflection off a Tynie defender in front of the keeper and wrong-footed him as it soared past into the goal.
Tynie did manage to reduce the deficit before half-time as Fraser Munro played in a ball from the corner and found Alex McNaughton at the back post to score.
They came agonisingly close to equalising shortly before the break as Munro cut inside from the left flank and fired goal-wards, but his shot drifted across the face of goal and went out for a goal-kick.
The second half started the same as the first did with Porty in the ascendancy. They consistently had their opponent on the back foot, but were thwarted time and time again by Calum Barlow who was in inspired form between the sticks for Tynie and kept his side within striking distance.
The goal to seal the match came 10 minutes before the final whistle as Harris Reynolds fired home from the edge of the box, taking the final score to 3-1.
Longniddry Under-16s advanced to the Colin Greenhill Memorial Cup final – where they will meet Tynecastle – after overcoming Leith Athletic 3-0 in the semi-finals.
The match was closer than the scoreline might suggest as both teams were evenly matched on the pitch and had good chances to go ahead in the first half. Despite the numerous opportunities created by either side, Euan Donaldson was the only scorer in the opening period of play and Longniddry went into the break 1-0 up.
Leith came out with more purpose in the second-half and Sam Capes in the Longniddry goal was forced into making some sharp saves.
The second goal of the game was a scored on the break by Ramsey Letham. He used his pace to cause problems in the Leith defence and slotted the ball calmly past the goalkeeper.
Leith pressed hard but with the game almost over Ben Smith ran in from the right wing and fired the ball low to the keeper’s right-hand side.
Hutchison Vale Under-14s progress to their fifth cup final of the season after beating a tenacious Lochend FA 3-1 in the Jewel Miners Cup semi-final.
A fiercely-contested first half saw Lochend go into the break with a goal advantage courtesy of Jamie Bannerman.
Both teams continued to knock the ball about nicely in the second-half, but Hutchie began to take control as the match wore on. The visitors squandered several good chances before finally levelling the game through a mix up in the six-yard box which resulted in an own goal.
As the match progressed, the home side seemed to tire and Hutchie’s two substitues in James Clare and Michael Symmers helped secure the victory. They each set up Rayan Mohammed and his brace put the game out of Lochend’s reach.