Bradley, 32, dropped Rios twice in the ninth before finishing him off with just seconds left of the round to make a successful first defense of his second reign as champion at 147.
Pre-fight opinions about the outcome of the fight had changed dramatically when Rios weighed in two ounces over and looked extremely gaunt, which ultimately came to fruition when Bradley ended the fight in fine style.
As Bradley moves on to be considered for a trilogy fight with Manny Pacquiao, Rios announced that he will now retire from the sport at the tender age of 29. Weight struggles have haunted the Californian for his entire career and at this late stage it was hard to see where ‘Bam Bam’ could have taken his career.
In the co-feature, Vasyl Lomachenko moved to 5-1 by halting Romulo Koasicha in the tenth to defend his WBO featherweight belt and move on to a potential unification in the coming year.
Ryota Murata, Miguel Marriaga, Mike Reed and Egidijus Kavaliauskas all recorded victories on the undercard in Nevada.
