In a match already reduced to 49 overs-per-side and after Marlon Samuels blazed an unbeaten 106 in the home team's total of 261 for seven, Pakistan were set a revised target of 189 off 31 overs as a second shower of the day interrupted play when they were 68 for two off 17 overs yesterday.
Needing a further 121 off 14 overs, half-centuries from Mohammad Hafeez and skipper Misbah-ul-Haq sped the visitors to the target with one over to spare.
"Mohammad Hafeez and I realised that we just had to play normal cricketing shots and look for the odd boundary. It was a case of not panicking and just staying focussed on the target."
Following a tie in the third match two days earlier, Pakistan now have an unbeatable 2-1 lead going into the fifth and final match at the same Beausejour Stadium venue on Wednesday.
West Indies seemed a dejected bunch when they took the field after being told by the umpires of the revised target, and Pakistan capitalised, Hafeez and Misbah crashing 54 runs off five overs before home captain Dwayne Bravo tried to get his team back into the match.