Marla Kavanaugh received widespread criticism for her rendition of God Defend New Zealand in front of more than 33,000 fans at the Snapdragon Stadium in San Diego, California, on Saturday ahead of an All Blacks match against Fiji.
The public took to social media to say Ms Kavanaugh "completely butchered" the anthem and described it as "dreadful" and "embarrasing".
"First time ever I muted the anthem", one person said.
"I would’ve picked Stan Walker to sing our national anthem. He can reach those high notes and make us proud", another said.
When contacted, former Associate Prof in voice at the University of Otago Judy Bellingham said it was difficult to sing a national anthem unaccompanied in an operatic voice, though "the quality of [Ms Kavanaugh’s] voice was not what it used to be".
"[Ms Kavanaugh] and her sister were both wonderful singers.
"When you’re singing unaccompanied, it’s very, very exposed and so unfortunately she chose a very slow tempo, which didn’t help and has exposed the vibrato in the voice."
Assoc Prof Bellingham said using the term "wobble" was a rude way to describe what vibrato meant.
It was the vibration in the voice when a singer reaches for a note.
"When people say ‘she sounded like a cat caterwauling’ they’re not totally wrong, because the vibrato was so pronounced."
She was surprised when she heard the performance, she said.
"You compare that to the anthem sung at the All Blacks test in Auckland where they had the National Youth Choir of New Zealand, who were absolutely brilliant ... you’ve gone from one extreme to the other.
"I have heard some of the players themselves had to stop singing."
Dunedin Operatic stalwart Gladys Hope said Ms Kavanaugh did a good job because the national anthem was not an easy song to sing.
"We all love it because it’s about New Zealand, but it’s not the best song.
"She’s a classy singer, so maybe they should not have gone for somebody who was going to sing ... a more operatic sort of version — maybe people thought she was a bit posh."
She said if people thought they could sing any better, then they should give it a go themselves.
"It may look easy but it’s because the person who sings it makes it look easy."
She sang with Ms Kavanaugh’s mother, Kathi Craig Hopwood, and had known Ms Kavanaugh and her sister since they were babies, Ms Hope said.
"What I always liked about the girls is their successes have not gone to their heads. You can’t say that about a lot of people."
Ms Kavanaugh told the ODT last night she was not yet ready to talk about her performance.
The All Blacks won the game 47-5.
