LAS VEGAS — Floyd Mayweather Jr. was Money once again.

Almost dropped by a right hand in the second round, Mayweather rebounded to dominate Shane Mosley the rest of the way Saturday night to win an unanimous 12-round decision in their welterweight fight.

Boxing's biggest box office draw remained undefeated in 41 fights, but not before giving his fans and his corner a scare when a right hand to the side of his head buckled his knees a minute into the second, and he had to grab Mosley to avoid going down. Mosley landed another right later in the round, but the rest of the night belonged to Mayweather.

Fighting before a star-studded crowd that included Muhammad Ali, Mayweather never came close to dropping Mosley, but landed so many more punches that the outcome wasn't in doubt past the middle rounds. He had an answer for everything Mosley tried to do, landing right hands to the head seemingly at will as the fight progressed.

By the end of the night, Mayweather had put so many rounds in the bank that the only question was whether he would stop Mosley or be content to win a lopsided decision. Mayweather kept moving forward and continued to press the issue in a fight that wasn't in doubt.

"I wanted to give the fans what they wanted to see, a toe-to-toe battle," said Mayweather, who has been criticized for fighting too defensively. "It wasn't the same style for me but I wanted to be aggressive and I knew I could do it."

Two ringside judges scored it 119-109 for Mayweather, while the third had it 118-110. The Associated Press had him winning 117-110.

Ringside punch statistics were as one-sided as the scorecards. They showed Mayweather landing 208 of 477 punches to 92 of 452 for Mosley.

Mayweather made Mosley look every bit his 38 years as he landed sharp punches to his head, dominating a fighter who had vowed to turn the bout into the fight of the decade. Mosley tried his best, but couldn't match the speed of the 33-year-old Mayweather, who grew more comfortable with each passing round.

Mosley was a substitute for Manny Pacquiao, who was all but signed to meet Mayweather until a dispute over drug testing derailed the megafight. Instead, Pacquiao beat Joshua Clottey on March 13 in Dallas and is now campaigning for a seat in congress in his native Philippines.

"If Manny Pacquiao can take a blood and urine test then we have a fight," Mayweather said. "If not, no fight."

Mosley almost ruined a lot of Mayweather's best-laid plans when he landed the big right hand in the second that brought the fans at the MGM Grand Arena to their feet. They chanted "Mosley, Mosley," as he followed Mayweather around the ring, landing another good right hand before the bell rang to end the round.

But it was Mosley's last hurrah. Mayweather came out in the third round and began landing some shots of his own, while Mosley couldn't find his mark.

"I caught him with my big right hand and I tried to move around but by that time he was too quick and I was too tight," Mosley said. "After the right hand I thought I needed to knock him out and I needed to do it sooner than later. But I couldn't adjust and he did."