Daniel Tardivel struck in added time to give St Peter a 4-3 quarter-final win over Grouville in Jersey's Trinity Shield.
The 91st-minute winner was the first time St Peter had been in front after earlier equalisers from John Tardivel, Jamie Mourant and Adam Le Cornu.
Jonny Gough and Charlie Petulla (2) netted for the hosts.
St Peter will now travel to St Brelade in the final four on Tuesday, 27 December.
The annual tournament sees Jersey-born players competing for either the parish they live in or the parish their parents lived in when they were born.