The 30-year-old right-armer has fashioned an impressive but brief international record, particularly in T20 cricket.
In 19 T20s for the Black Caps, he has captured 23 wickets at an average of 18.26 and an economy rate of 7.03.
Given those quality performances it is surprising the Otago Volts seamer has had to wait so long between opportunities.
He has become a perennial understudy — a role Matt Henry is awfully familiar with.
Henry got stuck carrying the drinks for years when Trent Boult, Tim Southee and Neil Wagner dominated the test side.
The comparison has certainly not been lost on Duffy.
"I’ve had some great conversations with him about this over a glass of wine" Duffy said.
"You don’t want that to be your role. You want to be the guy starting.
"But we’ve talked a lot about how to make the most of it."
Duffy’s role as the back-up seamer with the Black Caps means he actually has not played a lot of cricket this summer.
It can be hard to stay motivated when you are "bowling to a mitt".
"Obviously, you want to play every game.
"It can be a little niggly at times, don’t get me wrong.
"But I enjoy being away on tour.
"I feel like you feed off the guys and you learn and grow together, even if you’re not playing."
The lack of game time can take away the edge, though. That was evident when he returned from the test series in India and played in a Plunket Shield game for Otago.
He was poised on 299 first-class wickets and 30-odd overs later he still needed one more wicket to get to 300.
"I probably got a bit lazy in my training because you’re just bowling to a mitt in the middle a lot of the time.
"I guess it was a good lesson for me because then I went away [to the Champions Trophy] and I was a little bit more diligent."
He certainly has come back sharp.
Duffy took four for 14 in the opening T20 against Pakistan to help set up a nine-wicket win at Hagley Oval on Sunday.
Game two is in Dunedin today at the University Oval.
The forecast looked dire but has improved.
Black Caps captain Michael Bracewell will be just as relieved about that as Duffy.
Bracewell began his career with Otago as a top order batter, before shifting to Wellington and reinventing himself as an all-rounder.
He still has family in Dunedin, so it will be a special day for him to captain his country in his old home city.
The Black Caps’ flight into the city was cancelled yesterday, so they had to bus from Christchurch.
Duffy avoided the long bus trip. He had always planned to drive back with his partner.
"I actually got to sleep in and set off on my own leisurely time, so I’ve had a blinder."
Maybe the former Otago captain will have another blinder today.
T20 international
Dunedin, 2.15pm today
New Zealand: Tim Seifert, Tim Robinson, Mark Chapman, Daryl Mitchell, Mitchell Hay, Michael Bracewell (captain), James Neesham, Zakary Foulkes, Kyle Jamieson, Ish Sodhi, Jacob Duffy, Will O’Rouke, Ben Sears, Finn Allen.
Pakistan: Abdul Samad, Hasan Nawaz, Irfan Khan, Mohammad Haris, Omair Yousuf, Usman Khan, Salman Agha, Shadab Khan, Jahandad Khan, Khushdil Shah, Abbas Afridi, Abrar Ahmed, Haris Rauf, Mohammad Ali, Shaheen Shah Afridi, Sufiyan Muqeem.
