They showed plenty of character in the middle of the park with Katie Duncan and Annalie Longo at their industrious best. But, for all their toil, the Tony Readings-coached side in their black strip could not break down a determined USA defence.
The underdogs had their first chance of the night when left winger Betsy Hassett controlled on the edge of the area but could not link up with striker Amber Hearn in the final moments of the first half.
The USA began the second half in the same way as they started the night - in goal-scoring fashion. American forward Alex Morgan, who has hurt the New Zealand team on a number of occasions, found space inside the penalty box and hammered a low shot past Erin Nayler at her near post. Morgan continued her red-hot form in 2016 by netting her 12th goal of the year and fifth in Olympic play.
Morgan's goal a minute after half time was a body blow to the Kiwis' chances of a comeback and, from there, the favourites were always in control of the match.
Throughout the 90 minutes, New Zealand did not create a clear goal-scoring opportunity but Hearn did have a sight of the target in turning and volleying wide five minutes after the break.
Readings looked for some spark from the bench and livewire forward Sarah Gregorius entered the fray for midfielder Katie Bowen on the hour mark. Vice-captain Duncan was forced from the field in the 72nd minute after a nasty body check to her ribs and was replaced by recent centurion Kirsty Yallop in the midfield.
Shortly after Duncan departed, the USA could have made it three. A pin-point free kick from Heath caused Nayler problems and the ball bobbled free from her arms but Rebekah Stott was alert and on hand to clear the danger.
The last 20 minutes saw the USA control possession but a corner kick from Yallop did create chaos in the box in the 80th minute. A goal-mouth scramble ensued by no one could get a telling touch as New Zealand's hopes of getting on the scoresheet faded out.
With goal difference likely to prove crucial in determining which countries make it past the group stages, it was vital for the Kiwis to make it through additional time unscathed and they did just that to post a two-goal defeat.
They will now look to bounce back on Sunday morning (NZ time) when they face World No. 24 Colombia, who play their opening game against France later today, at the same venue.