Anthony Joshua was taken to the 10th round before stopping the durable Carlos Takam and retaining his WBA and IBF heavyweight titles in front of an estimated 75,000 fans in Cardiff on Saturday.
The referee moved in to stop the fight after Joshua caught Takam with a hook-uppercut combination and was moving in to land more blows. The Frenchman shook his head in disgust and many in the crowd jeered the decision.
At the end of an uncomfortable evening for Joshua, during which he might have broken his nose through a second-round clash of heads, the British boxer earned a 20th straight win that likely set him up for a unification fight in 2018 with either WBO champion Joseph Parker or WBC champion Deontay Wilder.
Takam was fighting at 12 days' notice - as an injury replacement for Kubrat Pulev - and lived up to his reputation as a tough opponent, absorbing big shots by Joshua and making himself tough to hit with his movement. Takam took an eight count in the fourth round after toppling from a left hook by Joshua, and fought on with a cut above his right eye that twice required treatment.
Joshua was taken beyond seven rounds for only the second time in his pro career. The other time was the 11-round fight against Wladimir Klitschko in April.
"I was trying to break him down round by round," Joshua said. "Unfortunately, the ref stopped it. I think people want to see Takam unconscious on the floor. That was where I was trying to get to. I don't have control over the ref's decision."
Takam (35-4-1) was cheered by the crowd after the fight at Principality Stadium, Wales' national sports arena.
"I don't know why the referee stopped the match," he said.
Joshua was fighting at the heaviest weight of his professional career - 254.8 pounds (115.6 kilograms) - and predicted a grueling slog against an experienced opponent that gets in close and works the body.
Takam caught Joshua with some shots, but they didn't have enough power to hurt the champion. Still, Joshua looked frustrated at times, and even showboated in the seventh round by walking into Takam's range with his arms out and head down, then shaking his head as Takam threw a punch.