The parish side finally relinquishing the silverware they won for the first time ever last season.
Paul Aitken, Jordan Docherty and Ruben Legge netted for the Scots and Richard Russell, who opened the scoring midway through the second half, and Jason Byrne for Grouville.
The chase for second place continues.
First Tower and Jersey Wanderers both won; Trinity were without a game while Grouville were beaten.
Tower slammed nine past St John condemning the losers to Reserves Division II football next season.
Ryan Durand (three), Michael Agrela (two), Chris Conning, John Rutter and Peter Vincenti netted for Tower, whose other goal was an own goal.
Wanderers returned with maximum points from St Clement where Duncan Prince hit a hat-trick and Neil Spacie a single for Wanderers.
Wayne Shales and Matt Scriven replied.
St Clement and Rozel Rovers remain in relegation trouble, Rozel going down 2-1 to St Paul’s at Les Quennevais.
Mark Ray and Luke Watson scored for the Saints and Tony Zonfrillo for the Rovers.
St Peter won promotion to Reserves Division I next season without having to kick a ball.
Sporting Academics missed their opportunity to go up following a 3-2 defeat away to St Lawrence.
David Fitton (two) and James McNaire notched for the Saints and Michael Perreira and Jamie Roberts for the Accies.
St Brelade won 2-0 at home to the Portuguese Club after goals by Danny Richardson and Nico Bisson.
St Martin/SCF are now three off the bottom after Sheik Omar Soner hit a hat-trick and Danny Harris a single in a 4-1 win against Beeches Old Boys.
The Old Boys’ consolation came courtesy of Pete Le Cuirot.
Rozel Rovers closed the gap on C Division leaders Grouville, who were without a game, to three points following a 5-0 win at Le Couvent against Sporting Academics.
Colin Roworth (three) and Sean Anderton were on target.
Jersey Wanderers defeated St Lawrence 4-1 at the Hockey Club with Ollie Thompson (two), Scott Slicer and Clive Richardson registering for the hosts and Chris Le Sueur for the visitors.
Tim Ward hit the only goal to give St Peter a 1-0 home win against St Clement while the mid-table clash at St Ouen ended in a four-all draw with St Brelade.
Dave Evans and Phil Faulkner hit doubles for St Ouen with St Brelade scoring through Rob Cambell, Neil Hacquoil, Andy McGinnigle together with an own goal.
Coca-Cola Combination, Div I Res: First Tower 9, St John 0; Grouville 2, Jersey Scottish 3; St Clement 2, Jersey Wanderers 4; St Paul’s 2, Rozel Rovers 1.
Div II Res: Beeches Old Boys 1, St Martin/SCF 4; St Brelade 2, Portuguese Club 0; St Lawrence 3, Sporting Academics 2.
Div C: Jersey Wanderers 4, St Lawrence 1; Rozel Rovers 5, Sporting Academics 0; St John scratched to Beeches Old Boys; St Ouen 4, St Brelade 4; St Peter 1, St Clement 0.
