Charlotte Edwards returned from injury to lead the tourists, who posted 115 for five after she won the toss.
Yet the Windies overhauled that with 19 balls to spare thanks to Stafanie Taylor’s 51 and 46 from Deandra Dottin, who together added an unbroken 78 in a much more one-sided game than the one between the sides decided by a super over two days ago.
Jenny Gunn, who had been filling in as skipper for Edwards in the last two contests, dismissed Kyshona Knight in the powerplay shortly before Holly Colvin, playing in her 50th T20 international, ousted Merissa Aguilleira, but Taylor and Dottin saw their side to an eventually comfortable victory.
Taylor also starred with the ball, snaring Lydia Greenway for a duck en route to miserly figures of 1-8 from four overs.
Greenway was the third of three wickets to fall in four powerplay balls after Shanel Daley had Danni Wyatt caught behind via a top edge and Edwards was comfortably run out by Shemaine Campbelle.
Sarah Taylor responded with a responsible 28, but Tammy Beaumont holed out off Shaquana Quintyne before wicketkeeper-batter Taylor was herself bowled by Stacy-Ann King as she failed to connect with a reverse-paddle in the closing overs.
Natalie Sciver, who cleared the leg-side boundary from the last ball of the innings, continued her impressive tournament with an unbeaten 36, but her and Gunn’s late-innings runs proved insufficient.
The teams now meet in three one-day internationals at Trinidad from Tuesday.