Gulbadin Naib had earlier provided the backbone of Afghanistan’s 182-6 with a pugnacious 63 off 35 balls.
The all-rounder struck three fours and four sixes at a strike rate of 180.00 as he shared stands with Rahmanullah Gurbaz and Sediqullah Atal.
Lockie Ferguson claimed 2-40 while Matt Henry, Jacob Duffy and Rachin Ravindra chipped in with a wicket each.
New Zealand looked in trouble when Mujeeb Ur Rahman removed Finn Allen and Rachin Ravindra for 1 and 0 respectively.
But Seifert and Glenn Phillips rebuilt with a third-wicket partnership of 74 before the latter was bowled by Rashid Khan for a 25-ball 42.
Seifert hammered back-to-back sixes off Mohammad Nabi – bringing up his half-century in the process – only to fall a couple of deliveries later to the experienced spinner when he holed out to square leg.
There would have been a few nerves when Mark Chapman departed for 28 but with Rashid and Mujeeb bowled out, Mitchell and Santner showed the required composure to complete the job.