West Indies started poorly on Thursday and looked set for a skittling until Roston Chase, who made 38, and Romario Shepherd, who blasted 36 off 22 balls, helped them to a respectable 140 all out.
Tim Robinson got the chase off to a strong start with 45 off 24 deliveries and his opening partner Devon Conway hit an unbeaten 47 to steer the Black Caps home with more than three overs to spare.
"I think we knew there might be a little bit in the wicket but our seamers up front again, taking wickets in the powerplay is always important in T20 cricket," said New Zealand skipper Mitch Santner.
"We've been challenged at times against a good team and we've come through some tough moments on these wickets when it does a bit. The way we've bowled has obviously been outstanding."
Santner won the toss and opted to bowl with his opposite number Shai Hope giving an indication of the approach of his batters by thrashing the first delivery of the match for six.
Kyle Jamieson removed Alick Athanaze caught and bowled in the second over, however, and player of the series Duffy further vindicated Santner's decision with three wickets at the cost of a single run in the third over.
Jimmy Neesham, who took three catches in addition to his 2-31, ended the innings in the 19th over when Jayden Seales departed for a two-ball duck with an injudicious swing of the bat.
"We need to be ready when the first ball is bowled. I don't think we were ready today but, as I said before, I've just got to commend the guys for the effort they showed," Hope said.
The West Indies continue their tour of New Zealand with a three-match one-day international series starting in Christchurch on Sunday followed by three Tests in December.
