Joshua stuck to his game-plan to deliver an emphatic 118-110 (twice) 119-109 points verdict in a manner which contrasted the controversy and chaos that has served to define this promotion.
If it was short on the five-knockdown thrills which shocked the boxing world in their first meeting in New York in June, it was emphatic vindication for Joshua of tactics required to repel Ruiz’s crude advances.
Speaking at ringside, Joshua told DAZN: "I have the utmost respect for Andy Ruiz who beat me fair and square in the first exam – I failed the first time but I came back and studied him and passed this time.
"This ranks second. The first would be my fight against Wladimir Klitschko – it means so much to me and I learned so much from that fight.
"I respect Wladimir so much and he still gives me so much advice. This fight ranks number two though."
Apart from sporadic exchanges in which Joshua looked in danger of being lured into the kind of fight Ruiz required to repeat his victory, the 30-year-old largely sailed home with the minimum of fuss.
"I know that my fans like to see me knock people out and I can do that but sometimes with certain fighters you have to box smarter," said Joshua.
"I understand what Andy brought to the table so I had to decapitate him in a different way."
In a bout which had been threatened with delay by a rare desert rain-storm moments before they took to the ring, Ruiz had banked almost entirely on landing another big left money-shot.
And although he enjoyed fleeting moments of success it became increasingly clear Ruiz, who weighed in more than a stone heavier than for their previous bout, was short on ideas to get through Joshua’s sharp and consistent jabs.
As feared, Ruiz admitted afterwards that he had barely trained for the rematch, surely undermining his hopes of a trilogy that he expressed at ringside.
Ruiz admitted: "It was his night. I don’t think I prepared as good as I should have. I gained too much weight but I don’t want to give no excuses.
"He won, he boxed me around but if we do the third, you best believe I will come in the best shape of my life.
"I thought I would come in stronger and better. But you know what, next time I am going to prepare better with my team. This time I tried to train myself at times to get prepared."
As if the bout needed any additional hype, opinion had been split over its outcome with many believing Ruiz simply had to land another of his crude left hands to win.
Joshua rewarded them which seldom deviated from the script as he skated out of trouble against a much heavier opponent whose extra luggage clearly minimised his chances of retaining his titles.
Both men were cut around their left eyes in the first two rounds and it took until the fourth for the bout to burst into life with an exchange on the bell which served as a timely reminder of the danger posed by Ruiz.
Racking up the rounds on the scorecards, Joshua nevertheless showed an occasional propensity to switch off, allowing Ruiz rare and tantalising glimpses of a repeat success.
Every time Joshua was drawn in close the momentum swung in Ruiz’s favour and a left-right combination in the ninth served as another example as the Mexican instantly responded by dragging the challenger into danger.
Ruiz showed his frustration in the bout’s final seconds as he stood in the centre of the ring beckoning Joshua to engage, and when the final bell sounded the Briton raised his arms to vindicate his emphatic victory.
Asked about the prospect of going on to face either Deontay Wilder or Tyson Fury, Joshua added "I have been speaking about these guys a long time.
"This time, when I had the opportunity to focus solely on Andy, my head is in the right place. When Wilder and Fury are really ready, they will make the call.
"Until then, I respect them but I won’t continue to call them out. I am making my own lane and if they want to be a part of that, they will call."