Josh Lamy-Coudrais struck deep in injury time as St Ouen beat St Brelade 1-0 to lift the Trinity Shield for the first time in 73 years.
With seconds remaining Shaun Heslop crossed from the left for Lamy-Coudrais to volley in.
St Brelade had gone closest in the first half when Seb Poole's dipping shot from 25 yards hit the crossbar.
After the break Lamy-Coudrais also hit the bar, with an overhead effort, before his stunning 98th-minute winner.
St Ouen manager Alan Ferey told BBC Radio Jersey: "We set our stall out to defend well particularly in the first half against the breeze.
"To score in the last minute is a dream really because there is just no way back for the opposition."
The tournament, which is the oldest in Channel Islands football, sees Jersey-born players compete for the parish they live in or their parents lived in when they were born.
St Brelade assistant manager Daryn Noble said: "Fair play to St Ouen, in the second half they came out and rallied.
"What a great goal to win a cup final."