Rain arrived shortly afterwards - with New Zealand on 64 for 2 after 14 overs - and only got heavier for the next hour.
That Pakistan warmed-up for this series with a comprehensive 120-run victory at the same venue would inspire confidence in the side that suffered a top-order disintegration on Saturday and eventually succumbed to a 61-run defeat (on DLS) in the rain-hit encounter.
It took a stubborn rearguard action from Pakistan's tailenders to rescue their innings, with a 70-run eighth-wicket partnership off 43 balls between Hasan Ali and Shadab Khan proving key.
Guptill ended the day on 86 off 71 balls, hitting five sixes and five fours, while Taylor's 44 came off 42 and included four fours.
But while they got Colin Munro (0) early and Shadab took a great catch to remove Kane Williamson (19), Pakistan had no answers after the break as Guptill quickly took the game - and potentially the five-match series - away from them.
Guptill make unbeaten 86 in the eight-wicket win.
Pakistan were 39-3 on a good batting wicket as Imam-ul-Haq (2), Azhar Ali (6) and Babar Azam (10) fell cheaply.
De Grandhomme has played 12 ODIs for New Zealand, making 214 runs at 35.66 and taking eight wickets at 48.37.
Earlier, a spirited fightback from Hasan and Shadab helped Pakistan to a respectable 246 for 9 despite being reduced to 141 for 7 at one stage.
Trent Boult (one for 54) and Tim Southee (two for 57) were parsimonious early, restricting Pakistan to 39 for two after nine overs before Mitchell Santner was introduced.
Amir and Ashraf claimed one wicket each.
"It was a very disappointing performance", Pakistan captain Sarfraz Ahmed said. After all, Pakistan lost to India in their opening game in the Champions Trophy, before turning their form around to end up with the title. Malik had been in good touch during the last ODI assignment against Sri Lanka in UAE, but doesn't boast of a good record in New Zealand.
With Pakistan on the ropes, Shadab Khan and Hasan stepped up, cracking 21 off an Astle over as they upped the tempo.