By Ryan Burton

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

Bradley 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, 32, was fast off the mark, landing a series of combinations in a big first round.

Rios, a former World Boxing Association lightweight champion, absorbed a big right in the second, but responded in a battling exchange.

He was doing good work in the third before a body shot from Bradley clearly rattled him.

"I saw that his body was soft. I hurt him early to the body," Bradley said. "I kind of wanted to get him not thinking about it for awhile, and then I went back downstairs."

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.