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.
"We didn't really play for the whole game as well as the way that we started. We had them 2 for 2 at one stage and we were flying - usually in those situations we continue to put the pressure on and continue to play well but after the first ten overs we just bowled quite poorly and our fielding wasn't to the standard it needed to be. They had a couple of good experienced players that looked very well organised and they had a good partnership leading the way and they put on a big total".
Next up is Suriname this evening, followed by Botswana and Shane Jurgensen says there's little room left for error.
"We need everyone on the park contributing and that's probably what we didn't quite have today. We had a few boys really step up and have a good day and then we had some of the other guys sort of had a bit of a bad day. If we win the next two games we will most likely be in the semi finals so that's why tomorrow is really important. If we don't win tomorrow then we've got to rely on other results and net run-rate. After today's heavy defeat that run-rate won't be real good so we need to try and make sure we win the next two games".
Vanuatu's in a much stronger position after beating the Cayman Islands.
Captain Andrew Mansale and Apolinaire Stephen each claimed three wickets as the Caribbean team were dismissed for 154, with Mansale top-scoring with 34 as Vanuatu reached their victory target with four wickets and ten overs to spare.
They will face Norway.