Undefeated Deontay Wilder stopped Gerald Washington in the fifth round to retain his World Boxing Council heavyweight world title.
The 31-year-old champion started poorly in front of hometown fans in Birmingham, Alabama, and was trailing on the scorecards when he sprang to life in the fifth round, knocking Washington down with a right-left combination.
"I said I wasn't going nowhere. I am still here. We are going to keep the fights coming," Wilder said.
It was the first fight for Wilder since he broke his right hand and suffered a torn right biceps muscle in an eighth-round stoppage of US veteran Chris Arreola in July.
Wilder, who won the title in 2015 with a unanimous 12-round decision over Canadian Bermane Stiverne, improved to 38-0 with 37 knockouts.
Despite being a fill-in opponent for Wilder, Washington gave the champ trouble in the first few rounds. Washington, who dropped to 18-1 with 12 knockouts, got the call after Wilder's planned opponent, Poland's Andrzej Wawrzyk, tested positive for a banned substance.
Wilder barely broke a sweat in the opening rounds as he threw just a handful of punches, mostly jabs.
He let Washington bring the fight to him, but in the fifth he landed a solid right to the temple of Washington and quickly followed it up with a left to the head that Washington tried unsuccessfully to block.
The victory sets the stage for Wilder to try and unify the heavyweight titles against rival champions.
Britain's unbeaten Anthony Joshua and Ukraine's Wladimir Klitschko meet April 29 in London for the World Boxing Association and International Boxing Federation titles while unbeaten World Boxing Organization champion Joseph Parker of New Zealand is set to face Britain's undefeated Hughie Fury on April 1 in Auckland.
"I am ready for Joseph Parker. Are they ready for me?" Wilder said.
On the undercard, Jarrett Hurd stopped Tony Harrison in the ninth round to win the vacant International Boxing Federation 154-pound title.
"It is a feeling like I have never felt before," said Hurd of the victory. "You got a new champion at 154 in Jarrett Hurd."
"We just wanted to wear him down, and in later rounds take him out."