New Zealand piled on 324 for six from their 50 overs, then restricted the West Indies to 233-8 to complete another lop-sided victory with only Saturday's final match in Auckland to come.
New Zealand opener Lou Vincent completed his second limited-overs international hundred with a brilliant 102 off 117 balls.
Nathan Astle (81 off 88 balls) and Stephen Fleming [ Images ] (67 off 59) both chalked up half-centuries.
Fleming gave himself an early mark to allow super-sub Jeetan Patel [ Images ] to join the game and later said he was surprised by the tourists' apparent lack of urgency with the bat.
"I'm not too sure what their tactics were (but) I never got the feeling that were they coming hard at us," Fleming told the New Zealand Press Association.
Vincent struck 10 boundaries and a six to reach his second ton after making 172 against Zimbabwe in Bulawayo last August, while Astle hit four fours and three sixes to follow up his century from Saturday's third match in Christchurch.
Fleming was also in aggressive mood, slamming six boundaries and four sixes as he and Vincent put on 106 in 19 overs for the opening wicket. West Indies had won the toss and sent the home team in to bat.
The tourists threatened to put the brakes on New Zealand's scoring when they dismissed debutant Ross Taylor [ Images ] (15), Scott Styris [ Images ] (five) and wicketkeeper Brendon McCullum [ Images ] (21), but not before the serious damage had already been done.
"In great conditions we achieved almost everything we wanted. It's not often you walk away from a game saying that," Fleming said.
"There's no complaints. We're now determined to win 5-0 which we would rate very highly as an achievement."
With the match as good as over, West Indies made little attempt to chase the runs. Morton faced 155 balls for his 110 while Sarwan faced 58 deliveries for his 42 and Chanderpaul 54 balls for 30.
L. Vincent c Ganga b Gayle 102
S. Fleming c Ramdin b D.R. Smith 67
N. Astle c Ganga b Gayle 81
R. Taylor run out 15
S. Styris c D.R. Smith b Gayle 5
B. McCullum c Sarwan b Bradshaw 21
P. Fulton not out 13
H. Marshall not out 2.
Extras: (b-2, lb-2, nb-1, w-13) 18.
Total: (for 6 wickets, 50 overs) 324
Fall of wickets: 1-106, 2-262, 3-274, 4-284, 5-290, 6-317
Did not bat: D. Vettori, K. Mills, S. Bond
Bowling: I. Bradshaw 10 - 0 - 74 - 1 (w-1) F. Edwards 10 - 4 - 23 - 0 D. Butler 6 - 0 - 57 - 0 (nb-1 w-2) C. Gayle 10 - 0 - 50 - 3 D. Smith 9 - 0 - 73 - 1 (w-5) W. Hinds 3 - 0 - 23 - 0 (w-2) R. Sarwan 2 - 0 - 20 - 0 .
C. Gayle lbw b Mills 5
D. Ganga c Mills b Styris 15
R. Morton not out 110
D. Ramdin c Styris b Mills 10
R. Sarwan run out 42
S. Chanderpaul c Patel b Mills 30
D. Smith c Styris b Vettori 1
W. Hinds st McCullum b Astle 0
D. Bravo c McCullum b Bond 3
I. Bradshaw not out 1.
Extras: (lb-3, nb-1, w-12) 16
Total: (for 8 wickets, 50 overs) 233
Fall of wickets: 1-8, 2-46, 3-64, 4-133, 5-212, 6-214, 7-221, 8-229.
Did not bat: D. Butler
Bowling: K. Mills 10 - 1 - 45 - 3 (w-4) S. Bond 10 - 1 - 43 - 1 (nb-1 w-2) S. Styris 9 - 1 - 53 - 1 (w-2) J. Patel 10 - 0 - 54 - 0 D. Vettori 10 - 0 - 32 - 1 N. Astle 1 - 0 - 3 - 1
Result: New Zealand won by 91 runs