The Briton suffered a stunning upset last June as Ruiz shocked the boxing world with a seventh round knockout at Madison Square Garden.
But Joshua righted that wrong with a tactically perfect performance to take back the IBF, WBA (Super) and IBF belts, securing a clean sweep of the judges' scorecards after dominating the 12-round contest.
Without hesitating to take the rematch, Joshua becomes just the fourth heavyweight in boxing history to reclaim his titles at the first time of asking, joining Muhammad Ali, Floyd Patterson and Lennox Lewis in that exclusive club.
Joshua knocked down Ruiz in the third round on that famous night in New York before four knockdowns ended his reign at the summit of heavyweight boxing in devastating fashion.
That night, the 2012 Olympian was made to pay for some rash decisions, coming up short when unwisely choosing to engage with the lightning fast Mexican.
This time around, Joshua fought the most disciplined performance of his career expertly devised by trainer Rob McCracken and his team, controlling the fight with his sublime jab and fleet-footed movement around the ring that Ruiz had little answer to.
Six months on from that night in New York, Joshua came in over 10lbs lighter - the basis for a sensational performance with the weight of the world on his shoulders.
There was the occasional moment where Ruiz looked to repeat history, troubling Joshua at the end of the fourth.
Joshua emerged composed however, getting his jab going again and maintaining the distance that would keep him in control and frustrate the champion.
Ruiz needed a knockdown as the fight entered its championship rounds - but it never looked close to coming as Joshua maintained his discipline to the final bell.
The celebrations had already begun as the scores - 110 118-110 and 119-109 - were read out. They will go on long into the night.
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