Anthony Joshua also adds the WBO belt to his title as he chases unification.
In front of 78, 000 capacity crowd, the fight at the Principality Stadium in Cardiff went to 12 rounds before Joshua was ruled the winner 118-110, 118-110, 119-109 by the three judges.
This is the Nigerian-Brit’s 21 win in 21 fights as he extends his winning streak although he failed to beat Parker by a knockout.
The 28-year-old has now added the World Boxing Organisation (WBO) belt to his International Boxing Federation (IBF) and World Boxing Association (WBA).
For Parker, this was his first loss in his 25-fight pro career.
It was a fight of few clean punches as boxers remained cautious throughout although Joshua was clearly dominant.
Joshua left a cut above Parker’s left eye in the third round before the New Zealand boxer managed to throw a few more punches.
In the middle rounds, however, Parker attacked more but Joshua defended well and in the 10th round the cut above his left eye got worse.
At the end of 12 rounds, it was an easy decision to make for the judges and Joshua described the win as ‘light work’.
“I was switched on, focused and went 12 rounds. It was light work,” said Joshua.
“This was about boxing finesse. I stuck to my word. ”
“I was beaten by the better man,” said Parker.
“It’s been a good experience being here and I’m thankful for the opportunity. I want to go back and come back stronger.”
There is a rematch clause for the fight, although Joshua as the option of facing American boxer Deontay Wilder or mandatory WBA challenger Alexander Povetkin.
Joshua is now chasing unification of the heavyweight titles and the much-anticipated fight against Wilder could be next.
Wilder holds the World Boxing Council (WBC) and could meet Joshua before the end of 2018.
“Wilder, let’s go, baby,” Joshua screamed in his interview inside the ring after the fight.