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Duffy's promotion comes after a couple of strong years in the various domestic competitions and an impressive performance for New Zealand A during a four-dayer against West Indies A in Mt Maunganui earlier this month.
The 26-year-old right arm seamer picked up six wickets in the match to further enhance his reputation.
"Gavin [Larsen, national selector] called and said, ‘you're in mate' and I didn't offer him much back. I was a bit speechless," Duffy told the Otago Daily Times yesterday.
"There were a couple of expletives in there. I was pretty fizzed. It is a dream come true and it is what you play for.
"This is why you ultimately play. You want to get to the next level and see what you've got against the big boys."
None of the players competing in the second test against the West Indies was considered for selection and Black Caps speedster Lockie Ferguson has been ruled out with a worrying back injury.
That helped pave the way for Duffy but he is keen to show what he has to offer.
"There are a lot of good bowlers in the country and you have to do something special to stand out, so if you get the opportunity, and there is every chance I could be carrying the drinks, you've got to grab it."
Duffy made his debut for Otago in a televised T20 game against Northern Districts at Seddon Park as a 17-year-old, so for a young man he has plenty of experience.
He took three wickets in his debut and, because he cuts such a relaxed figure, he gives the impression it is all easy. But Duffy has had to work hard throughout the years.
Otago coach Rob Walter dropped him for two months during the 2016-17 season.
The Southlander was essentially sent to bowling boot camp and asked to remodel his action. He took the setback well and emerged a superior bowler.
He shelved some pace but gained accuracy and has been tremendously productive for Otago.
Eden Park is a daunting place to play as a bowler. Duffy's team-mate, Anaru Kitchen, was kind enough to remind Duffy he had clipped the medium pacer for a few runs at the venue.
"He reminded me he hit me on to the second deck. It is a challenge but it will be awesome."
While Duffy is thrilled with his inclusion, one of the country's greatest batsmen has been left out. While the test players return for games two and three in Hamilton and Napier respectively, Ross Taylor has been overlooked.
Larsen told The New Zealand Herald leaving Taylor out was a hard call.
"This was, as you'd imagine, a very tough decision as Ross has been a consistent performer for us, but unfortunately we just couldn't find room in the squad for him due to the quality and form of the other batsmen."
Black Caps squads
For T20 series v Pakistan
Game 1: Mitchell Santner (c), Todd Astle, Doug Bracewell, Mark Chapman, Devon Conway, Jacob Duffy, Martin Guptill, Scott Kuggeleijn, Jimmy Neesham, Glenn Phillips, Tim Seifert, Ish Sodhi, Blair Tickner.
Games 2 & 3: Kane Williamson (c), Astle, Trent Boult, Conway, Guptill, Kyle Jamieson, Kuggeleijn, Daryl Mitchell, Neesham, Phillips, Seifert, Sodhi, Tim Southee.