Goals from Paul Banahan and John Rutter took the parish side to victory and help them close the gap on divisional leaders Jersey Scottish to three points.
Saints junior goalkeeper Matt Brookland pulled off a string of fine saves to deny the title-challengers a more confortable success.
Grouville moved up one place to fourth, seven points behind Trinity, after they beat Rozel Rovers 4-3 at Le Boulivot.
Grouville ran into a 4-1 lead shortly after the break only for the Rovers to fight back well and almost snatch a point deep into time added on for stoppages.
Scott Healey notched a brace for Rozel, his first – which made it 4-2 – a fine individual effort after he danced his way through Grouville’s defence to craft out his opportunity.
Jerry O’Shea also notched for the Rovers with Grouville on target through Alex Jefferies, Jamie Drummond, Luc Le Mière and Richard Stevens.
No change at the top of Division II as a result of the top three all winning.
Leaders St Ouen maintained their two-point advantage over Magpies and Jersey Nomads after beating St John 3-1 at St Ouen.
Tom Richardson bagged a brace for the hosts and fellow midfielder Andy Modral single.
Junior Stuart Daynes hit St John’s goal to make the score 1-1 at the time.
Magpies defeated Sporting Academics 5-1 at Les Quennevais to avenge a 4-1 defeat earlier in the season.
Steve Cumming hit a hat-trick for the ‘Pies together with singles by Matt Pamplin and Johnny Moynes.
Johnny Irwin replied.
Jersey Nomads returned 3-0 victors from St Lawrence where Paul Starkey scored twice and Daniel Pinho once.
St Martin/SCF moved up two places to fourth from bottom after winning 3-2 against Beeches Old Boys at the FB Fields.
Jason Harris (two) and Paul Stier were on target for the winners and Hamlyn Moon and Martin Roberts for the losers.
The Portuguese Club of Jersey are up to fourth after they beat bottom-placed St Clement 4-1 at Les Quennevais.
The Saints were undone by José-Manuel Vieira’s hat-trick and one from defender Artur Calaca.
Jamie Fraser replied.
First Tower retained their one-point lead at the top of Division I Reserves after Mark Lucas’ double helped them defeat newly-crowned JFA Willis Cup holders Trinity 2-1 away.
The home team netted through Gerard Meadows who was later sent off.
Grouville and St Peter, the latter with a game in hand, kept up the pressure with wins against Rozel Rovers and champions Jersey Scottish respectively.
Grouville won 4-2 at Le Couvent after two goals by Murray Dron and Darren Quintal and Chris Smith singles.
Lee Kent and Peter Hawley scored for Rozel.
St Peter defeated the Scots at St Peter with a Scottish defender netting the only goal when under pressure from Paul Dicker midway through the first half.
St Brelade went top in Division II Reserves following a 4-0 win at St John where Nico Bisson hit a hat-trick and Neil Hacquoil a single.
Coca-Cola Combination, Div I: Grouville 4, Rozel Rovers 3; St Paul’s 0, Trinity 2.
Div II: Beeches Old Boys 2, St Martin/SCF 3; Portuguese Club 4, St Clement 1; Sporting Academics 1, Magpies 5; St Lawrence 0, Jersey Nomads 3; St Ouen 3, St John 1.
Div I Res: Rozel Rovers 2, Grouville 4; St Peter 1, Jersey Scottish 0; Trinity 1, First Tower 2.
Div II Res: Beeches OB 0, St Clement 5; Jersey Nomads 6, Sporting Academics 5; Portuguese Club 2, St Lawrence 2; St John 0, St Brelade 4; St Martin/SCF 0, Magpies 2.
Div C: St Clement 2, Grouville 10.
Lloyds TSB Junior League, U18 Div I: Jersey Wanderers 1, First Tower 1; Sporting Academics 4, St Brelade 1; St John 1, St Paul’s 0.
Div II: Grouville 6, St Ouen 2; St Clement 3, St Martin/SCF 0.
