The annual contest brings together six leading players from each Island, with Marshall followed in the final positions by five Sarnians.
Marshall’s closest tussles were against Guernsey’s Phil Ogier and Phil Hunkin, both finishing 3-2, with the Ogier contest going to 12-10 in the fifth game.
The second-placed Jersey player was Tom Quinn in seventh.
The veteran beat Martin Sarre and only narrowly lost to Jeremy Powell.
Although Bobby Vincent failed to register a victory over a Guernsey player, his results against his fellow Jersey competitors earned him eighth spot.
Trevor Lefebvre finished equal on points with Quinn and Vincent but was placed tenth on countback, after beating both Powell and Hunkin at the weekend.
Barry Vibert was 11th and Simon Brindle, in his first inter-insular outing, 12th.
The best placed Jersey junior was Chris Corfield in fourth place, behind Guernsey winner Adam Langlois.
Corfield won a game against Langlois and also beat Matthew Stubbington and Ryan Perry.
Josh Band also beat Perry, but the latter placed seventh, with Luke Walker eighth, Band ninth, Craig Roberts tenth, Natasha Marriott 11th and Matthew Cooper 12th.
