Bryansford were crowned Blue September Kilmacud Sevens champions for the first time since 1994 at Glenalbyn this evening.
In an all-Down pairing, Brendan Corrigan's charges overcame their Mourne County rivals by 1-15 to 2-11 in a keenly contested decider.
Despite Bryansford getting a goal after 15 seconds from Ciaran Brannigan, Castlewellan came back strongly to hold a 1-7 to 1-6 interval lead, with Kevin Duffin netting a sixth minute goal.
Bryansford emerged strongly after the restart as points from captain Jim Magorrian, Chris Clark and Ciaran Brannigan gave them a two-point cushion.
Castlewellan cut the deficit to the minimum following a goal from their goalkeeper Colm Óg Crilly, but Bryansford held out to take a fifth-ever Sevens title.
Afterwards Jim Magorrian accepted the cup from Leinster GAA Chairman Martin Skelly, with Ciaran Brannigan named the Player of the Tournament.
Bryansford overcame fellow Down side Longstone by 3-10 to 1-14 in the semi-final, while Castlewellan overcame a six-point deficit to finish 2-11 to 1-8 winners over Eoghan Rua, Coleraine in the other last-four encounter.
Earlier, reigning champions St Galls, Antrim crashed out at the quarter-final stage after succumbing to a 3-10 to 0-6 defeat to Castlewellan.
Six of the eight quarter-finalists were from Ulster with Dublin duo Kilmacud Crokes and Ballymun Kickhams flying the flag for the rest of the country.
Host club Kilmacud Crokes were beaten by 4-8 to 0-13 by Eoghan Ruadh, Coleraine in their last-eight encounter.
It took penalties to separate Longstone and Ballymun Kickhams after two late Ambrose Rogers goals ensured a 2-8 to 0-14 full-time score-line.
The Down side outscored their Dublin opponents by 2-0 to 1-1 on penalty kicks.
Meanwhile, Bryansford beat Glenullin, Derry by 3-13 to 1-10.
At the Eirgrid Ratoath Intermediate Sevens Meath side Nobber beat Tir na nOg, Randalstown by 1-12 to 1-6 after extra-time at Sean Eiffe Park.
The sides were tied at 1-6 to 0-9 at the end of normal time, with Nobber claiming the only goal.
Meanwhile, St Jude's (A) captured the Bord Gais Energy All-Ireland Junior Sevens title thanks to a 0-10 to 0-9 extra-time win over St Jude's (B) at Templeogue.
In the semi-finals St Jude's (A) registered a 2-11 to 0-3 win over Offaly's Clonmore Harps, with their club colleagues 1-7 to 1-6 winners over Drumaness, Down in the other semi-final.
Caherlistrane took the Shield title following victory over Europe in the final.
Caherlistrane had beaten St Mary's Cahirciveen by 5-5 to 4-5 in the semi-final, with Europe 2-6 to 0-3 victors over St James, Cork in the other last four encounter.