It was no more than New Zealand deserved after an impressive all-round display, although Ghana will be disappointed as they could have likewise taken the points if they had shown Christensen's composure in front of goal.
New Zealand goalkeeper Nadia Olla put on what must be one of the best performances of her career so far, the highlight being a pair of outstanding saves in quick succession late in the first half to keep the match scoreless at the break.
Further up the pitch, Paige Satchell was in inspired form and caused constant problems for the Ghana defence with her direct running and silky skills.
One such charge by Satchell created the best opening of the game at that point in the 13th minute, the Rotorua-raised midfielder breaking down the right and cutting the ball back for Isabella Coombes, who couldn't beat goalkeeper Agyei and showed her frustration at passing up the excellent opportunity.
Leon Birnie's side had another just moments later when Jasmine Pereira played Martine Puketapu in one-on-one with Agyei but dragged her low shot agonisingly wide.
New Zealand were almost made to pay for those misses when a delightful ball was floated into their box but was powerfully volleyed over the bar at close range by Jane Ayieyam in the 27th minute.
After such an entertaining first half, the second spell didn't quite live up to expectations and there were fewer clear-cut opportunities, although Ghana again could have taken the lead when Olla did well to block a Wasila Diwura-Soale effort at point-blank range in the 72nd minute.
Christensen had come on just seconds earlier as Birnie continued his search for the winner but it was Pereira - another New Zealand player to catch the eye with a commanding display - that almost provided it, the Football Fern doing well to create space for herself wide in the area before fizzing a volley narrowly across the face of goal as full-time approached.
The New Zealand bench all had their faces buried in palms after going so close to taking a late lead but were soon on their feet in rapturous celebration as Christensen did exactly what she had been brought on to do, breaking the hearts of the Black Princesses but putting the Kiwis in a strong position going into their remaining Group C matches against the United States and France.
"It happened so fast so it's hard to describe but I just tried to put it in the back of the net and luckily it went in," Christensen said.
"I'm so happy for the girls, we did so well to pull it off in the end. It was very hot and tiring but we played really well and it was a real team effort."
New Zealand's next match at the PNG Football Stadium in Port Moresby is on Thursday night against the United States, who drew 1-1 with France in the day's other Group C game.
