After putting Guernsey into bat, Viliame Manakiwai dismissed both openers without scoring to have their opponents reeling at 2 for 2.
But a century stand for the third wicket between Oliver Newey, who made 129, and Tim Ravenscroft, who blasted 74 from 63 balls, laid the platform for Guernsey's imposing total of 287 for 7.
Fiji never got close - Jone Wesele top-scoring with 20 as they were rolled for just 99 inside 38 overs.
Shane Jurgensen says they let Guernsey off the hook.