Joshua was forced to go the distance for the first time – but was unanimously declared the winner with a wide margin on the judges’ scorecards: 118-110 twice and 119-109.
After his win, Joshua told Sky Sports: “My strategy was to stick behind the jab.
“I was switched on and I was focused, Joseph Parker is a world champion and I said this was about boxing finesse.
“What you can’t forget is that I am the unified heavyweight champion of the world.”
Both fighters had stepped into the ring undefeated at Cardiff’s Principality Stadium and the win extends Joshua’s perfect pro record to 21 victories from as many bouts.
Joshua had won his previous 20 fights with knockouts but struggled to land clean shots on Parker, as a crowd of 78,000 watched on.
Parker, a New Zealander, said afterwards that he would “love to have another go”.
He said: “I lost to the better champion tonight.
“It has been a good experience being here, and I am thankful for the opportunity.
“I want to go back and come back stronger. I have no regrets – we take it on the chin.
“We will be back again and we will work harder to come back.
“He (Joshua) is a good big man and was better on the day.”
As for Joshua’s future plans, Deontay Wilder holds the other main heavyweight belt, the WBC’s, and could meet Joshua before the end of this year.
“I’m not into the hype, let’s get the business done,” Joshua said after the bout.
“Let’s see what the future holds, I’m down for whatever, whenever.”
Then he screamed: “Wilder, let’s go baby!”
The American responded overnight, posting a video to Twitter and Instagram, making it clear he is ready to fight Joshua and sympathising with Parker, saying: “What a robbery… WOW‼️ @joeboxerparker great job Bro omg don’t apologize you did nothing wrong. True champion. @anthonyfjoshua, I ACCEPTED 100%.
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“P.S. Take AFRICA off your Arm. They’re warriors. You from UK brotha.”
Another British heavyweight, Tyson Fury, also posted a video in which he dismissed Joshua and Parker as a “pair of bums”.