Andy Ruiz Jr. turned the sport of boxing on its head Saturday night in New York, stunning the heavily-favored Anthony Joshua via seventh round knockout and putting the rest of the division on notice. Ruiz, a 15-to-1 underdog at the start of the night, overcame a third round knockdown to badly hurt Joshua late in the third and eventually finish him off via TKO in round seven.

Joshua (22-1, 21 KO) started the fight by methodically working his jab against the shorter, portlier Ruiz (33-1, 22 KO,) who looked like a bus driver fighting a bodybuilder in the ring against the Adonis-figured Joshua. After two rounds of feeling each other out, Joshua landed a counter left hook that sent Ruiz to the canvas. Joshua, clearly thinking Ruiz was on his last legs, moved in for the kill. But instead of ending the fight Joshua walked into a left hand that staggered him and eventually sent him to the canvas. Ruiz, who has diminutively quick hands for this unathletic body type, jumped on Joshua and sent him to the canvas again after a barrage of punches. Joshua was in bad shape but survived the round after being saved by the bell.

Joshua spent most of the fourth and fifth frames regaining his legs following the knockdowns, and looked to be back in control in round six. But Joshua, who at 6'-6 and 247 lbs towered over Ruiz, got sloppy again in round seven. Ruiz, used a barrage of quick punches to send Joshua to the canvas twice more before the referee had seen enough, calling off the action for the safety of Joshua.

The win makes Ruiz, a previous heavyweight journeyman, the unified heavyweight champion of the world, holding three of the four major world titles. Deontay Wilder, the WBC champion, holds the fourth. Ruiz is the first fighter of Mexican descent to win a major heavyweight championship.

Ruiz wasn't even supposed to get a chance at Joshua. The fight was originally given to Jarrell "Big Baby" Miller of Brooklyn. But in the lead up to the fight Miller tested positive for three separate banned substances, and Ruiz stepped in on short notice to keep the card on schedule. Miller is now left to question what could have been.

After the fight both Joshua and his promoter Eddie Hearn indicated that they would exercise their contractual right to an immediate rematch with Ruiz. Hearn indicated the rematch, which would once again be for three of the four major heavyweight belts, would take place in the United Kingdom in either November or December. Joshua was gracious in defeat, telling DAZN's Chris Mannix that it was Ruiz's night and anything can happen in heavyweight boxing. He stayed in the ring following the loss and smiled while posing for pictures with Ruiz, who had just taken his belts.

Joshua's loss puts a question mark on the assumed unification fight between him and Wilder. Both men have been posturing for the fight for the better part of two years, with both sporting world titles and undefeated records prior to Saturday. Wilder was quick to take to social media and criticize Joshua following the defeat, saying his career was built on lies and gifts.