Imam, retired hurt on 16, was beaten for pace and bounce as the short-pitched delivery rose sharply.
Later, the Pakistan Cricket Board confirmed on Twitter that Imam's scans were clear.
He was immediately sent to a hospital for CT scans and the team management said they would monitor him for the next 48 hours. "He joined the team and will remain under observation of Team Physio".
The New Zealand middle order had no answers to Shadab Khan (1-25 from 10 overs) and the under-fire Mohammad Hafeez (1-31 from 10), with a remarkable 21-over drought between boundaries putting Pakistan firmly on the front foot.
With the win Pakistan broke a four-year losing streak of 12 consecutive ODIs against the Black Caps, starting with a 3-2 defeat in the UAE in 2014.
"A bit of scrapping that got us a total", he said.
New Zealand squad remains unchanged from the side that beat Pakistan by 47 runs in the first game. The play had to stop five balls later as an ambulance waited near a sidescreen for Imam, who had to be stretchered in it, to take him to the hospital.
Undeterred by Imam's injury, Zaman added a quick 101 for the second wicket with Babar Azam who made a 50-ball 46 before both fell in the same Ferguson over.
Taylor hit three boundaries and a six for his 43rd half-century in ODIs.
Worker struggled for his 50-ball knock of 28 before he played all around to off-spinner Hafeez and was clean bowled while Afridi made its 4-73 by clean bowling Tom Latham off a sharp yorker.
That came after captain Kane Williamson's luck ran out early in his innings when he was dismissed for just one run due to a deflected drive into his stumps for a rare run out. Nicholls was finally bowled in the 38th over by Hasan Ali who finished with 2-59.