The noise woke Naketoatama's sister, who believed the men had set off her car alarm on Wyllie Rd.
Naketoatama, who made his boxing debut in 2000, left his home to confront the pair and pursued them down several Papatoetoe streets.
Once he caught up to the duo on George St he launched a "pre-emptive strike" and levelled Hetherington, knocking him to the ground, Judge Blackie said.
"He didn't know what had hit him because to use [Hetherington's] words, 'the lights had gone out', he was seeing stars."
Naketoatama then clobbered Margison.
"In falling to the ground as a result of your blow he hit his head on the concrete and was seriously injured," the judge said.
Margison, a life member of Otahuhu United AFC, was in a "life or death situation" and in desperate need of medical care.
"Even though this man was lying on the ground and bleeding profusely - you got in a car, driven by your sister, and departed the scene," the judge told Naketoatama, who was aided by a Samoan translator.
After Hetherington came to, he attempted to help his mate, who was still unconscious on the ground.
Paramedics finally arrived and Margison was taken to hospital, however, he was diagnosed with serious brain injuries, and his family were told there was a chance he would die.
Naketoatama was arrested five days later on April 15.
"These two men had been struck by a man who had been a professional boxer," Judge Blackie said.
"The force of a blow by [Naketoatama], whether it be a punch, a glancing punch, or even an open handed slap would have considerable force behind it."
The judge said attacks to the head are always considered "more serious" than to other parts of the body.
"Perhaps it was your boxer's reaction? One significant blow to the head," the judge asked Naketoatama.
"They posed no threat to you at all."
Any expression of remorse from Naketoatama was also too late, Judge Blackie said, adding it should have been shown at the scene by helping the two injured men.
Naketoatama's partner, brothers, and other family members were all in court for the sentencing.
Victim: 'I have lost my freedom'
Margison, still suffering the long-term effects of his injuries, told the court he can no longer work and his sporting life had been robbed from him.
"It was a major part of my life - I loved it ... Before the assault I enjoyed being helpful, before the assault I walked everywhere."
Doctors have told Margison he can no longer play contact sport, and he has also lost his senior coaching positions due to his injuries.
For 10 years he coached the Clendon Cats women's team and had been the goalkeeping coach for Papatoetoe AFC women's teams.
Margison now "find[s] talking very difficult", and often has no memory of what he has said to his friends.
"I am not the type of person to go and sit in a corner and cry but there have been times I have wanted to," he said during his victim impact statement, while being supported by members of his family in the courtroom.
"I am not allowed to drink alcohol anymore. I never considered myself a heavy drinker but I liked to socialise."
A tearful Margison also said his relationship had broken down a few months after the attack.
"It was upsetting and hard when she said she was not going to be part of my life and part of my recovery."
The effects of the attack have also been tough on his two children - son Jay, a tank commander in the army, and daughter Kendall, a businesswoman.
Margison's 86-year-old mother now lives with her son to help care for his injuries, while he hasn't returned to his job as a Fed-Ex driver since the attack.
One shining moment in his life after the attack, he said, was watching his daughter marry last December, he tearfully smiled.
Judge Blackie said Margison has "not fully recovered and is unlikely to fully recover" from Naketoatama's blow.
