Nelson, Australia (BBN)-Ireland added West Indies to their list of World Cup scalps with a magnificent four-wicket triumph in Nelson.
Lendl Simmons (102) shared 154 with Darren Sammy as the Windies recovered from 87-5 to post 304-7.
But Ireland openers Will Porterfield and Paul Stirling put on 71 and Stirling (92) added 106 with Ed Joyce, reports BBC.
Joyce hit 10 fours and two sixes in 84 and Niall O'Brien 79 not out as Ireland won with 25 balls left, their fourth World Cup win over a Test nation.
Having beaten Pakistan in their first World Cup in 2007 and England in the 2011 tournament, Ireland were almost considered favourites from the outset against a Windies side eighth in the ODI rankings, skittled out for 122 by England in a warm-up match and rumoured to be in disharmony following the omission of Kieron Pollard and Dwayne Bravo from their squad.
Some intrepid fielding and accurate seam bowling from Ireland after choosing to field quickly led to two wickets falling in the eighth over.
Big hitting Gayle and Marlon Samuels both launched towering straight sixes before both were dismissed by 22-year-old George Dockrell in the 22nd over, the left-arm spinner with figures of 3-23 at one point.
Sammy unleashed some innovative strokes, often with ferocious power, in a thrilling partnership with Simmons, who accelerated stylishly as West Indies became the fifth successive team in the tournament to post in excess of 300 when batting first.
But far from overawed, the Irish openers punished some loose bowling in a fluent 13 over stand.
Man-of-the match Stirling hit three sixes in his pugnacious innings and was within eight of his sixth ODI hundred when, suffering from severe cramp, he edged behind in the 28th over with 128 still needed.
With the Windies looking ragged and forlorn, Joyce effortlessly guided the Irish within 32 of the target and despite three wickets in 17 balls, O'Brien, badly dropped on 38 by Jason Holder, saw them home.
Ireland, coached by former West Indies batsman Phil Simmonds, uncle of Lendl, next face the UAE in Pool B on 25 February.
BBN/AS-16Feb15-12:00pm (BST)