LAS VEGAS -- Floyd Mayweather Jr. got the title he wanted, but not the impressive win he needed.

In his first fight as a lightweight, Mayweather took the WBC 135-pound title from Jose Luis Castillo in a foul-filled bout that did little to showcase the talents of either boxer.

Mayweather won 115-111 on two scorecards and 116-111 on the third ringsisde card in a decision that was loudly booed by the pro-Castillo crowd. The Associated Press had Mayweather ahead 115-111.

The unbeaten Mayweather was moving up after successfully defending his 130-pound title eight times and was a 7-2 favorite despite never having fought as a lightweight.

He won by using his jab effectively and staying away from Castillo much of the fight, tactics that did nothing to endear himself to the crowd or give him the impressive win he said he needed to establish his popularity.

"Tough fight. Tough guy," Mayweather said. "I'll fight him again."

A bitterly disappointed Castillo said he would welcome a rematch after a fight he thought he had won.

"I was robbed," Castillo said. "I knew it was a close fight but I thought I had it won."

Mayweather (28-0) showed little of the power that had gotten him 20 knockouts in his previous 27 fights, partly because he was on the move most of the fight trying to win rounds by using his left jab and some occasional counter punching.

He said later that he injured his left shoulder his last day in training and couldn't throw his left hook at all.

"The fight was a lot closer because of that," Mayweather said.

The fight was marred by both fighters hitting on the break and after the bell, and the rough tactics cost both of them points. Castillo was penalized in the eighth round for hitting Mayweather with a left hook on the break, while referee Vic Drakulich took a point from Mayweather in the 10th round for using his elbows.

The two continued even after the bell sounded to end the 12th round, with fighters trying to keep the fight going.

Mayweather fought cautiously in the early rounds, as though he might be concerned about the power of an opponent who was bigger than any he had ever fought.

Castillo (45-5-1) was clearly the favorite of the crowd of about 5,000 at the MGM Grand hotel-casino, despite Mayweather's fighting reputation. The crowd cheered loudly for the Mexican champion, chanting his name as he stalked Mayweather around the ring.

Castillo had defended his lightweight title three times before, but never against a fighter like the talented Mayweather. He pressed the fight and took it to Mayweather, but missed far more punches than he landed.

Castillo rarely caught up to Mayweather, and when he did, he was often slow in throwing punches. At the end of the fifth round, he caught Mayweather on the ropes and landed a left and right and Mayweather responded by smiling at him.

Castillo kept pounding away at the body after the bell rang to end the fifth round, and Drakulich had to pull him off of Mayweather, who followed Castillo back to his corner smiling and offered him a hand as if to congratulate him.

It wasn't until the 11th round that Mayweather decided to stand and trade punches with Castillo, and the two went at it flat-footed in the middle of the ring for most of the round, with Mayweather seeming to get the best of it.

Mayweather, who weighed in at 134 pounds, earned $2.2 million, while Castillo, 134½, was paid a career-high $1.1 million.

In the co-main event, Stevie Johnston moved into contention for a title shot with a 12-round majority decision win over Alejandro Gonzalez in a WBC elimination fight.

The win by Johnston, who lost his lightweight title to Castillo, moves him into the No. 1 position in the WBC rankings.

The left-handed Johnston (34-2-1) landed more punches than Gonzalez, but drew boos from the crowd for refusing to mix it up with the former WBC featherweight champion.

Johnston, whose training was interrupted when he was jailed for a week in Denver for not paying child support, won the fight on two ringside scorecards while the third judge had it a draw.

"I knew those girls were trying to bring me down so I had to concentrate extra hard to show them they didn't have that effect on me," Johnston said.

Johnston said he was able to train somewhat while in jail.

"I was doing pushups and body work and they let me run up and down the stairs," he said.