Hard-working Morriston withstood a spirited Lampeter fightback to lift the Swalec Bowl.
Tries in either half from Sean Richards and Steffan Jones saw the Lan Fields club bring home the Bowl to their part of Swansea, which has been gripped by Millennium Stadium fever ever since the Division Three South West side reached the final.
Morriston coach Steven Thomas admitted his side were lifted by the sense of excitement which has filled the town in the weeks leading up to the club's Cardiff date.
He said: "The likes of our boys would have never have thought they would be able to play on the Millennium Stadium pitch.
"It has really lifted the town, people have been talking about it non-stop and I have had people coming up to me shaking my hand in the street."
Morriston took the lead through Gareth Jones's penalty on two minutes before winger Sean Richards ran virtually the length of the Millennium Stadium pitch to score the opening try.
Richards picked up on a lose pass and ran unchallenged from his 22 to touch down beneath the posts on ten minutes.
Jones converted and kicked a further penalty but Lampeter came back with three long range penalties from Huw Thomas to end the half trailing by four points.
In the second half, Morriston introduced Steffan Jones on 51 minutes and within three minutes he had scored the game's second try, latching onto good work from Chris Cullen and crossing to make the game 20-9 after Gareth Jones's conversion.
But Lampeter fought back and on the hour mark, centre Mark Saunders finished off a move on the right wing to go over in the corner.
Lampeter pushed forward, and Thomas kicked another penalty to make the game 20-17, but try as they might they could not get the score they needed.
"I felt we used the touchline as our friend, which helped us see off a Lampeter side that was really strong in the second half," said Morriston coach Steven Thomas.
"We are now aiming for promotion next season and to go on and win the Swalec Plate!"
In contrast, Lampeter coach Huw Williams, who recovered from a quadruple heart bypass two years ago to lead the Division Three West outfit to Welsh rugby's home, was magnanimous in defeat.
He said: "We were disappointed with how the game ended but someone had to lose and what an occasion it was."