"The toughest squad selection was clearly around the spinner," said coach Gary Stead.
"That basically came down to the balance of the side and with the four-strong pace attack going so nicely we wanted to have a spinning allrounder as an option for that No 7 position.
"It's really unfortunate for Ajaz, who has overcome his calf injury, but the all-round ability of Santner is our preferred option for this series. The fact Ajaz hasn't been able to have any game-time in the lead-up was also a concern."
Santner's preferred status raises the possibility he will sneak into the all-rounder's role ahead of incumbent Daryl Mitchell for the Bay Oval Boxing Day test. While a fifth bowler has barely been needed this summer thanks to the rule of Tim Southee, Trent Boult, Neil Wagner and Jamieson, the Mt Maunganui pitch might need something a bit different.
Last summer he picked up three vital second-innings wickets when New Zealand defeated England at the ground. He also scored his only test century in the same match.
The only other decision management will have to make is whether Will Young keeps his place in the XI, though it is unlikely he has done enough to tip Tom Blundell out given that he is not a natural opener.
New Zealand were handed a boost with the unavailability of Babar Azam and
Imam-ul-Haq. The pair are yet to recover from their thumb injuries. Mohammad Rizwan will lead the side in Azam's absence. It is a blow for the neutral however as the classy Azam is one of the easiest batsmen on the eye in cricket today.
New Zealand enters the series chasing a 2-0 victory that will keep them in the hunt for a World Test Championship final at Lord's in June, a quest that has gained impetus with India's heavy defeat in their first test against Australia.
"Our rise through the test rankings is a great achievement, but we know the challenge is now to back that up against a quality Pakistan side," Stead said.
Pakistan will surely offer more resistance than a West Indian team that looked as if it had forgotten how to play test cricket.
Although the formats remain poles apart, Pakistan's seamers have showed enough during the T20 series to suggest that if they win the toss on a green top — as the Windies did at Hamilton and Wellington — they will not similarly waste conditions.
They will need to if they are to put a stick through this New Zealand team's spokes.
Since they lost to South Africa in Wellington in March 2017, the test team have been on home roll unprecedented in New Zealand cricket history. In the 15 matches since, they have won 11 and drawn four.
Included in the tallies are traditional heavyweights England and India, so it hasn't all been bullying minnows. Pakistan are, like New Zealand, considered somewhere between a giant and a minnow.
Where New Zealand's good and bad times tend to be cyclical, Pakistan's can occur within the space of a series.
NZ Squad:
Kane Williamson (c), Tom Blundell, Trent Boult, Kyle Jamieson, Tom Latham, Daryl Mitchell, Henry Nicholls, Mitchell Santner, Tim Southee, Ross Taylor, Neil Wagner, BJ Watling, Will Young.
