Ruiz recorded a monster upset, knocking down Britain’s Joshua four times to take the World Boxing Association, International Boxing Federation and World Boxing Organization titles.
Ruiz came into the fight as a massive 20-1 underdog. But he won it in the middle of the seventh round when the referee stopped it at 1:26 of the round after the fourth knockdown.
Ruiz, sent to the canvas once himself, knocked Joshua down twice in the third round and twice more in the seventh.
Joshua had a massive height and reach advantage as he weighed in at a chiselled 255 pounds compared to the portly Ruiz, who beefed up to 268 pounds compared to 250 for his most recent fight.
Ruiz, who has won four fights in a row, looked fearless and poised while Joshua — who had won all 22 of his previous bouts — never seemed to recover from the first knockdown early in the third.