The West Indies were all out for 269 on the penultimate ball of their innings, while Ireland were dismissed for 245 in reply on Saturday (Sunday AEDT).
Brooks just missed becoming the second West Indian to score an ODI century on debut, after Desmond Haynes, the team's new selector.
Brooks and captain Kieron Pollard, who made 69, combined for a 155-run partnership after the hosts had been reduced to 4-62 in the 19th over. Offspinner Andy McBrine took two wickets in two overs.
The Irish mainly bowled well, with medium-pacers Mark Adair and Craig Young taking three wickets each.
The West Indies went 12 overs without a boundary and Brooks and Pollard picked their moments.
Pollard's four sixes came in the space of six balls, including three consecutive off McBrine over midwicket, long on and backward square leg. Pollard was out in the 42nd over, top-edging a pull to the long on boundary off Young after 69 off 66 balls.
Brooks went next in the 45th, his fine 93 off 89 balls, including nine boundaries and three sixes. He was lbw to Adair.
Ireland, coming off a shared series with the United States in Fort Lauderdale, started without Paul Stirling, Simi Singh and Ben White - all infected with coronavirus.
After William Porterfield was out for a duck and McBrine retired hurt on 34 after being hit in the helmet grill, captain Andy Balbirnie and Harry Tector set a solid platform, even as the run rate was creeping up.
But after Balbirnie was hit on the grill by Odean Smith, he was out three balls later in a new over by Romario Shepherd, poking at a ball and edging behind.
Out for 71 off 94 balls, Balbirnie's exit ended a stand of 103.
Tector was out in the next over, trying to cut and top-edging Smith to Roston Chase on the boundary. Tector made 53 off 68 balls.
With both set batsmen gone by the 38th over, Ireland never recovered.
Shepherd and Alzarri Joseph took three wickets each.
The series stays in Kingston on Tuesday and Friday, followed by a one-off Twenty20.
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