In what were chaotic scenes in the ring at Trusts Stadium in Waitakere, Williams said he would have won the fight if it had been in the United States.
Two judges awarded the the score 90-100, and the third scored it 94-97.
"No disrespect, but if that fight was in America... this decision is ridiculous," Williams shouted in the interview afterwards.
"Let's do a rematch."
Parker said: "It's not up to me, we are the fighters, let's leave it up to the judges to decide."
Williams added: "I promise to knock you out in six rounds next time." Parker replied by asking him why he couldn't do it first time around.
Asked about the result, which appeared fair to the majority of observers and the vocal crowd, Parker's trainer Kevin Barry said: "You don't have to be a boxing expert to know he [Williams] lost every single round."
It was a bizarre finish to a fight which Parker dominated over the 10 rounds but failed to land the knockout blow as he had promised to do at the weigh-in.
The victory, in front of several New Zealand personalities, including Warriors Shaun Johnson and Manu Vatuvei, and former All Black Jonah Lomu, means Parker retains his WBA PABA and WBO Oriental heavyweight titles and takes his record to 11 victories from 11 fights.
Parker was relaxed in walking to the ring, kissing his mother Sala on the way, but it was a spiteful fight at times, with Williams landing a big right hand on Parker after the bell which signalled the end of the third round. Parker's trainer entered the ring and remonstrated with Williams, with the Bahamas' fighter's cornerman replying in kind.
Referee Brad Vocale handed Williams a warning, and also warned him for a low blow earlier in the round.
Both men were friendly towards each other at the end, but Williams kept up a running commentary to referee Vocale before launching into his tirade.
Parker had begun the interview afterwards by praising his opponent, saying: "Sherman Williams is a very experienced fighter and has a very hard chin. Those punches would have knocked most people out."
Williams had promised to press Parker throughout the fight but left his run late, perhaps allowing for his age and 120kg weight. His best round was the sixth, when he had Parker in the corner and struck him twice with his overhand right.
It was one of the more difficult fights Parker has had in his career, and a far cry from his last bout, against American journeyman Keith Thompson in Pennsylvania in August.
Parker, who went into the bout ranked 11th in the world by the WBA organisation, will next headline a Fight for Life event in December in Hamilton.
In a significant result on the undercard, Reece Papuni beat Sam Rapira to claim the New Zealand National Boxing Federation lightweight title with a fourth-round TKO.
Both fighters went to the ring undefeated, with Papuni knocking down Rapira three times, twice in the fourth round, and all with his right hand.
- Patrick McKendry of APNZ
