Shamarh Brooks marked his ODI debut at the age of 33 with a fine 93 while skipper Kieron Pollard hit a fluid 69 as the West Indies posted 269 all out.
In reply, the Irish were well-set at 165-1 with captain Andy Balbirnie making 71 and Harry Tector hitting 53.
However, once they fell in the space of eight balls, the required run-rate crept up and the West Indies claimed a key opening victory in a three-match series which forms part of the qualifying route to the 2023 World Cup.
Romario Shepherd finished with 3-50, including the key wicket of Balbirnie, while Alzarri Joseph claimed 3-55.
