Sol3 Mio singer Moses MacKay says the American singer who muddled her way through the British and New Zealand national anthems at the Kiwis rugby league defeat in Denver may have lost sound from her ear monitor.

Crystal Collins performed both God Save The Queen, God Defend New Zealand and E Ihowā Atua [te reo Māori version] before the clash at Mile High Stadium today.

"I couldn’t believe it, I was like, 'poor girl'… It was bad, it was real bad," Mr Mackay said.

"People don't understand that so many things can happen.

"It kind of sounded technical and a bit like she didn’t know the words," he said.

Mr Mackay, who was contracted to perform the national anthem for New Zealand during the All Blacks series against France, says his ear piece cut out during his performance in Dunedin last night.

"When you’re standing ready to sing you have these inner-ears in, and you can hear the track or you can hear yourself sing… Last night of all times my ear (piece) cut out."

Mr Mackay said it's a "weird" experience and singers subject to it can only hear an echo.

"Imagine singing in a room and then covering your ears and trying to sing, it’s an odd thing but I just knew, ‘It feels like I’m singing, my voice is coming out, I’m gonna carry on," he said.

Mr Mackay said leading the national anthem in front of thousands of people is daunting but a moment of pride.

He said it didn’t sound like the American singer Crystal Collins gave New Zealand’s national anthem the respect it deserved.

"I've learnt since a kid… the mana of singing the anthem, having the whole nation sing along you and in the whole stadium is a bit different," he said.

"The meaning behind singing the national anthem is the coming together of one."

Commentator of the game for Sky Glen Larmer said it was a horrendous and appalling performance.

"I don't know how to describe it other than being an absolute train wreck.

"It was a disappointing look for this occasion, which was an important one for international rugby league."

Mr Larmer said event organisers failed to get an important element of the match right.

"I don’t recall anything that bad, I mean she sounded so unsure of herself, not familiar with the song, it's like she hadn't heard the song before."

Armchair music critics have been quickly on the attack on social media.