Timothy Bradley battered Brandon Rios en route to a ninth-round technical knockout in a lopsided welterweight bout that had a dejected Rios announcing his retirement.

Bradley on Saturday retained his World Boxing Organization world title, improving to 33-1-1 with 13 wins inside the distance with the triumph at the Thomas & Mack Center in Las Vegas.

Fighting for the first time under the guidance of trainer Teddy Atlas, Bradley was quick and aggressive against a challenger who struggled to make the 147-pound weight limit.

Bradley sent Rios to the canvas with a left to the body in the ninth. Rios beat the count, only for Bradley to unleash a barrage that had him down again and referee Tony Weeks calling a halt at 2:49 of the round.

Rios, 29, wasn't contemplating any future in the ring after falling to 33-3-1, with 24 knockouts.

Rios' longtime trainer, Robert Garcia, supports his fighter's decision to retire.

"He was flat. Maybe trying to make weight may have drained him. But if the body's not there, there's nothing you can do about it. I support Brandon's decision 100 percent," Garcia said.

Rios said he was not going to place himself at risk by continuing to fight.

"I'm done. I had a wonderful career. But I think it's time for me to hang up the gloves. My body doesn't want to cooperate anymore, and I don't want to get beat up anymore," Rios said.

"He hit me with a perfect shot up the middle and an equally perfect shot to the side of the head. The better man won. I have no excuses."