Deontay Wilder shook off injury to retain his World Boxing Council heavyweight world title as bloodied challenger Chris Arreola failed to answer the bell for the ninth round.
In front of euphoric home fans in Birmingham, Alabama, on Saturday, Wilder remained undefeated in 37 fights, notching his 36th victory inside the distance with the technical knockout.
Arreola had absorbed immense punishment when his corner told they referee they wanted to call a halt.
He was bleeding from a cut on the bridge of his nose opened in the first round, and his left eye was nearly swollen shut.
Wilder dropped Arreola in the fourth round, and after the challenger made the count of eight -- assuring the referee he was good to go on -- Wilder rocked him again at the bell.
The win looked all the more impressive when Wilder said in a post-fight interview he had broken his right hand and torn a muscle in his right arm.
"I wanted to give you guys a knockout, but I broke my hand and I tore a muscle," Wilder told the in-ring interviewer as a cornerman applied an icepack to his right biceps.
"Wilder is going to get checked out at a local hospital tonight and will be seeing a specialist this week to assess the damage to his right hand and right bicep," promoter Lou DiBella said.
From the fifth round on Wilder barely used his right, but punished Arreola with stinging lefts, sending him wobbling back to his corner at the end of the seventh.
Arreola, who fell to 36-5 with one draw and 31 knockouts, fell to 0-3 in heavyweight title fights -- all three of them knockouts.
He took the fight on short notice after Wilder's scheduled title defense against Alexander Povetkin in May was undone by Povetkin's positive test for meldonium.
The cancellation of that bout has resulted in lawsuits from the Povetkin and Wilder camps, but the champion showed no sign of the distractions in the ring.
He was quick to call out the other heavyweight world title holders, saying he'd take on Britain's International Boxing Federation champion Anthony Joshua or the winner of a title rematch between Britain's Tyson Fury and Ukrainian Wladimir Klitschko.
"My goal is to unify the division," Wilder said. "Whoever's got those belts, that's who I want."