Boroughmuir inflicted another dose of BT Cup final misery on shock troops Dundee at Murrayfield.
Full-back James Reilly emerged as the hero of the Edinburgh outfit, bagging a crucial try and landing a sequence of pinpoint kicks.
Their Second Division opponents battled with spirit and bravery.
But, as in their defeat 12 months ago by Glasgow Hawks, Dundee just did not have enough in the tank to win Scotland's main cup trophy.
Dundee had deservedly broken the deadlock in the fifth minute thanks to a confidently-struck penalty from Barry Jones.
But Calum Cusiter - brother of Scotland scrum-half Chris - nipped across for a Boroughmuir try after a patient spell of phase-building in the danger zone.
James Reilly added the conversion and found the target again from the widest possible angle after the second try after flanker Angus Martyn reacted to a loose ball.
Dundee breakaway forward Allan Brown executed a textbook pick and charge to reply, Jones slotting the extra points from wide out.
Boroughmuir made a hash of throwing to the tail of the line-out and Mark Jenkinson pounced to snap up the loose ball.
He plunged over in glee - only for referee Graeme Hannah to leave everyone in the national stadium confused as he chalked it off.
But Dundee reduced the deficit to a single point on the stroke of half-time with a Jones penalty from long-range after foul play by Reilly was spotted by a touch-judge.
Boroughmuir flanker Ben Fisher powered over in the corner following a series of powerful mauls after the break, Reilly making a difficult conversion look simple.
Dougie Gray peeling off the back of a maul to score after a penalty line-out as Dundee hit back.
But Muir's fitness and experience began to tell.
Reilly sent over a penalty then added the goal to his own try set up by a perfectly-weighted short pass from hooker Dave Cunningham.
Dundee set up a tense finale when substitute Jonathan Alston found a gap to score in the corner, with Jones converting.
But Reilly eased the Muir jitters with a penalty before Rory Couper skidded in for the fifth try.