Oleksandr Usyk turned his sights on rival heavyweight world champion Tyson Fury on Sunday after beating Britain's Anthony Joshua on a split points decision to retain his WBA, WBO, IBF and IBO belts in Jeddah.
The "Rage on the Red Sea" in Saudi Arabia was a rematch of a fight in London in September, which the Ukrainian won on a unanimous decision to take Joshua's belts, but with more intensity and emotion.
Usyk appeared comfortably ahead as the final bell rang at the King Abdullah Sports City Arena but the American judge surprisingly awarded the fight 115-113 to Joshua.
The British and Ukrainian judges decided 115-113 and 116-112 to Usyk.
The victory took the 35-year-old's professional record to 20 fights undefeated while Joshua, 32, suffered a third defeat in what could prove a watershed in his career.
Joshua, who had held aloft the Ukrainian flag with Usyk as they waited for the decision in what seemed an acceptance of defeat, then had an uncharacteristic meltdown.
He took two of the belts, dropping them as he left the ring and headed for the dressing room before turning around and stepping back between the ropes to take the microphone and address the crowd.
"Usyk is one hell of a fighter. That’s just emotion," declared the Briton.
"For this guy to beat me tonight, maybe I could have done better but it shows the levels of hard work he must have put in, so please give him a round of applause as our heavyweight champion of the world."
Following the celebrations Usyk's thoughts turned to the next chapter and another Briton to beat, although WBC champion Fury has declared himself retired.
"I am convinced he wants to fight me. I want to fight him. And if I'm not fighting Tyson Fury, I'm not fighting at all," Usyk told the crowd through a ringside interpreter.