Having suffered one of the biggest upsets in boxing history back in June in New York City, AJ came back and regained his titles in Saudi Arabia.
Anthony Joshua and Andy Ruiz Jr took to the ring in the rematch in Diriyah.
Ruiz had stopped Joshua in the 7th round when both boxers squared up at Madison Square Garden in June.
But on Saturday night, the 30-year-old out-boxed his opponent from first bell to last and Ruiz ended the fight with a cut above his left eye while Joshua barely bore a mark of the contest.
Ruiz Jr had been a late replacement for Jarrell Miller when he stunned the Brit in June but after a full camp preparing for his opponent, the new world champion had answers for every question he was asked.
He will now await the result of the February 22 rematch between Tyson Fury and Deontay Wilder and attempt to make a fight with the winner to unify, at last, the heavyweight division.