Dwayne Smith snared four wickets for 29 runs as Zimbabwe, chasing 267 from their allocation of 50 overs, were dismissed for 162 in 49 overs.
West Indies, who go on to face a much stiffer examination against India, also completed back-to-back victories by five wickets and 98 runs in the first two matches at St. John's, an 82-run win last Sunday at Georgetown, and a 10-wicket triumph last Wednesday at Gros Islet.
The third ODI at Georgetown was abandoned without a ball bowled because of rain, and the rain-affected sixth match here on Saturday was also abandoned with no result.
Brendon Taylor struck five fours on Sunday to top score for Zimbabwe with 43 from 82 balls and Vusimuzi Sibanda gave him support with 42 off 82 balls that contained two boundaries.
They added 59 for the third wicket, but there no substance and no stability from the rest of the batting which quickly folded.
Ramnaresh Sarwan had hit half-dozen boundaries in the top score of 91 from 114 balls, as West Indies totalled 266 for eight from their allocation of 50 overs after they chose to bat in ideal conditions.
The elegant right-hander added a vital 71 for the second wicket with compatriot Shivnarine Chanderpaul and put on 67 for the third wicket with West Indies captain Brian Lara.
Chanderpaul struck four fours and one six in 45 from 69 balls and Lara counted two fours and three sixes in 40 off 38 balls.
Tawanda Mupariwa was the most successful Zimbabwe bowler with three wickets for 44 runs from his 10 overs.
Mupariwa's new-ball partner Blessing Mahwire collected two for 49 from his 10 and leg-spinner Ryan Higgins snared two for 52 from his 10.
West Indies now tackle India in a series of five ODIs and four Tests, and Zimbabwe contest a triangular ODI series in Trinidad, starting on Tuesday, when they face Bermuda and Canada, two associate member nations that have qualified for the 2007 World Cup in the Caribbean.