Anthony Joshua has been taken to the 10th round before he stopped the durable Carlos Takam to retain his WBA, IBO and IBF heavyweight titles.
The referee moved in to stop the fight after Joshua, who likely won every round, caught Takam with a hook-uppercut combination and was moving in to land more blows.
Takam shook his head in disgust and many in the Cardiff crowd, estimated to be about 78,000, jeered the stoppage.
At the end of an uncomfortable evening for Joshua, the British boxer earned a 20th straight win that likely set him up for a unification fight in 2018 with either Joseph Parker or Deontay Wilder.
"I don't know why the referee stopped the match," Takam said. "I don't think they should have stopped it. I want the rematch if Anthony gives me it."
The fight was Joshua's first since his epic 11-round tussle with Wladimir Klitschko in April, and just the second time he has been taken beyond seven rounds in his pro career.
Joshua has surpassed Mike Tyson's record of 19 consecutive knockouts.
"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 fighting at 12 days' notice as an injury replacement.
Unbeaten champion Joshua opened up a nasty cut above 36-year Takam's right eye in the fourth round and knocked down the durable France-based Cameroonian late in round.
It was far from a straight-forward night for Joshua in the Principality Stadium as the 28-year-old appeared to suffer a broken nose in the second round after an accidental clash of heads.
Takam caught Joshua with some shot but they didn't have enough power to hurt the champion.