This result was New Zealand boxer Parker's first defeat in his 25-fight pro career.
Parker and his team took issue with referee Giuseppe Quartarone, even claiming the Italian couldn't speak English, but Joshua wasn't having a bar of it.
The judges scored it 118-110, 118-110 and 119-109 in his favor, leaving Joshua just one belt - Wilder's WBC title - away from becoming the first undisputed champion since compatriot Lennox Lewis in 2000.
With the fight done and dusted, Joshua admitted he doesn't bear any ill will towards Parker - and made sure to check-in with his mother Sala right after the fight. "Get him in the ring and I'll knock him spark out".
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Joshua added: "That is 21 professional fights with six world title fights in it. I stuck to my word and I controlled it behind the jab, the counter-punches".
AJ eventually emerged from the 12 rounds as the unanimous victor, earning him Jospeh Parker's WBO strap and taking one huge step to unifying the heavyweight division.
Forget the hype; Joseph Parker is a world champion so I knew he would be determined.
Tony Bellew, who faces David Haye in a repeat of their heavyweight grudge match on May 5, in London, added: "Every time they wanted to have a fight he was in there".
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Wilder who will likely be Joshua's next opponent, however, believes the 28-year-old does not fight like Africans. I want to go back, train hard and come back stronger. That particular matchup is slated to be one of the biggest heavyweight fights of all time, and could very well take place sometime next year in Joshua's home of England.
Parker's rally lasted two rounds, before Joshua adjusted sharply, reasserting a comfortable distance and landing with a short left hook and right uppercut on multiple occasions when Parker tried to attack.
Joshua looked typically confident and carried that energy into the ring, often keeping his opponent on the back foot with an accurate ramrod jab and the Kiwi was muscled to the ropes by a crunching combination in the third.
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