Sunday's was West Indies' second victory on the trot following an 11-run win against the same opponents in a Twenty20 International match on Friday to draw the two-match series. (Agencies)
West Indies started in a hurry with openers Smith and Powell attacking the Irish bowlers and sharing the century partnership for the first wicket.
Smith, who was drafted in the team to replace an injured Chris Gayle, made good his opportunity and raced to 55 off 53 balls.
Ireland got back into the match dismissing Kirk Edwards and Darren Bravo in quick succession, but Powell stayed around for a well played 57 off 72 balls.
Captain Dwayne Bravo had a quickfire 35 to bring the West Indies closer to their target.
Marlon Samuels and Darren Sammy stayed at the end to carry the West Indies home.
Earlier, Ireland recovered from 78 for 4 to reach 202 all out, thanks mainly to a 45-run stand between Gary Wilson (62) and Kevin O'Brien (22).
Stuart Thompson also frustrated the West Indies' bowlers with a stubborn 33.
Jason Holder (3/34), Dwayne Bravo (3/36) and Nikita Miller (2/30) were the pick of the bowlers.
Ireland, with one win from three matches on tour of the Caribbean, will switch attention to the International Cricket Council (ICC) World Twenty20 Tournament in Bangladesh.
West Indies will now play England in a three-match ODI series in Antigua followed by three T20s in Barbados.
Ireland 202 in 49.2 overs (Gary Wilson 62, Stuart Thompson 33, William Potterfield 25; Jason Holder 3/34, Dwayne Bravo 3/36, Nikita Miller 2/30)
West Indies 205 for 6 in 36.4 overs (Kieran Powell 57, Dwayne Smith 55, Dwayne Bravo 35, Marlon Samuels 26 not out; Stuart Thompson 2/17)
Sunday's was West Indies' second victory on the trot following an 11-run win against the same opponents in a Twenty20 International match on Friday to draw the two-match series.