Joseph Parker has fulfilled his dream of becoming a WBO boxing world champion but says he's already looking ahead towards heavyweight domination.

The 24-year-old Kiwi edged foe Andy Ruiz Jr by majority decision in Auckland on Saturday, becoming the first person in his country's history to secure a heavyweight title.

Victory came by the slenderest of margins, with two judges awarding him victory by 115 points to 113, and the third awarding a draw.

"It was a very close fight, he brought his A-game and I knew he would because he trained hard, lost some good weight, showed some speed and power," Parker said.

The south Aucklander started the fight slowly and struggled to puncture Ruiz's defence but grew into the contest as it wore on, dominating the closing rounds.

In the end it was Parker's superior fitness and punching power that told, as his Mexican-American opponent began to tire and endured repeated flurries.

"When we used that jab, and punished him from that outside, we knew we won those rounds," Parker said.

"I felt that when I was using my jabs, everything flowed better, (but) when I didn't use it, I allowed him to close the gap and throw his punches."

Both fighters promised an open, offensive battle in the days leading up to the bout and didn't disappoint, showing plenty of willingness to throw early combinations.

Ruiz dominated the opening rounds until Parker managed to hit his 27-year-old opponent with a left-hand blow in the fifth round and swing momentum his way.

He went on to dominate much of the second half of the fight, particularly the ninth and 10th rounds, and secure enough points to scrape home.

Trainer Kevin Barry said the match panned out just as he anticipated, with Parker's fitness making him most dangerous at the fight's climax.

"You saw Joe landed flush punches on his chin and Andy comes straight back immediately with three or four of his own," Barry said.

"Joe waited a little bit long before he got his double jab working, but Andy's a skilful guy, we knew it was going to be a big test."

The title win caps a stunning ascent for Parker, who has been crowned world champion after just four years as a professional boxer.

He is now likely to seek a unification fight overseas next year, or a bout with former champion Tyson Fury when he has recovered from substance abuse.

Duco Events director David Higgins declined to rule out hosting a title defence in New Zealand, mentioning Dunedin's Forsyth-Barr Stadium as a potential venue.

But Parker said he was just keen for a rest, before hitting his straps again next year in the quest to become the first undisputed heavyweight champion since Lennox Lewis.

"This is just the start, now we've won this, we want to dominate the heavyweight division, that's our goal, to win, keep winning, dominate and unify those belts," Parker said.