The big Southlander ran through the West Indies tail to help roll them for 167.
He finished with five for 34 in just his second test.
Canterbury’s Matt Henry did a lot of the leg work, though.
The 33-year-old bowled brilliantly following the drinks break in the afternoon session.
He nicked off Roston Chase and Justin Greaves in the space of four balls.
But Duffy stole the limelight with a rush of wickets late in the day.
New Zealand were 32 without loss at stumps and lead by 96 runs in a low-scoring game.
Earlier in the day, the home side could not add to their overnight tally of 231 for nine.
Zak Foulkes nicked off but changed skins quickly and took a wicket with the first ball of his spell.
West Indies opener John Campbell might have got away with the thick edge, but Will Young dived hard to his left and reeled in a stunner at third slip.
Alick Athanaze got a ripper from Henry. It nipped back and rattled the bails from their moorings, leaving the West Indies in a mire at 10 for two.
Tagenarine Chanderpaul — son of West Indies great Shivnarine Chanderpaul — seems to love wading through mud.
He has picked up some of his dad’s quirky habits.
He walks across the stumps and closes off a lot of scoring options.
But he values his wicket and he dug in.
Shai Hope is a one-dayer dasher who is up there with the best. But he has a poor test record for a player of his calibre. He set about improving it.
The pitch was like lava, though.
The pair jumped around and nearly got crispy feet.
The short ball was decidedly uncomfortable for them.
Devon Conway dropped a couple at leg slip. Chanderpaul was the beneficiary both times.
The West Indies limped through to lunch at 68 for two.
Hope posted his sixth test half-century after the resumption and the partnership was building slowly.
Duffy forced a breakthrough. He dug in a short one and Hope (56) gloved it through to Tom Latham, who was filling in at wicketkeeper for the injured Tom Blundell.
Henry is the master when there is a little bit in the pitch and it proved the downfall for Chase. The batter got a millimetre or two of wood on it and Latham pouched it.
The pair also teamed up to account for Greaves. The edge was a healthier one, the result the same.
It was a magnificent spell, but can someone tell Henry that Movember ended last month?
The Windies resumed the final session on 120 for five.
Chanderpaul’s vigil came to a poetic end on 52. Conway cut off a cracking pull shot with a brilliant catch.
He had dropped the left-hander twice previously and lay on the ground counting the ways he felt relieved.
Following a brief break for rain, Duffy nabbed two quick wickets to leave the visitors teetering.
He then pushed them over the edge when he swung the ball past the swinging bat of Jayden Seales and bowled a timid-looking Ojay Shields.
NEW ZEALAND
First innings 231
WEST INDIES
First innings
J Campbell c Young b Foulkes 1
T Chanderpaul c Conway b Foulkes 52
A Athanaze b Henry 4
S Hope c Latham b Duffy 56
R Chase c Latham b Henry 0
J Greaves c Latham b Henry 0
T Imlach c Latham b Duffy 14
K Roach not out 10
J Layne c & b Duffy 0
J Seales b Duffy 2
O Shields b Duffy 0
Extras (10b, 6lb, 7nb, 5w) 28
Total (75.4 overs) 167
Fall: 1-1, 2-10, 3-100, 4-106, 5-106, 6-140, 7-157, 8-157, 9-167.
Bowling: M Henry 22-7-43-3, Z Foulkes 18-7-32-2, N Smith 15-6-39-0; J Duffy 17.4-7-34-5, M Bracewell 2-1-3-0, R Ravindra 1-1-0-0.
NEW ZEALAND
Second innings
T Latham not out 14
D Conway not out 15
Extras (2b, 1w) 3
Total (no wkts, 7 overs) 32
Bowling: K Roach 3-0-13-0, J Seales 2-0-8-0, O Shields 1-0-5-0, R Chase 1-0-4-0.
