LAS VEGAS - Floyd Mayweather's self-styled claim as "the best ever" apparently was shared by the judges who gave him a clearcut unanimous decision over Manny Pacquiao Saturday night at the MGM Grand Garden. The victory improved his record to a perfect 48-0, leaving him one short of the 49-0 record achieved by undefeated heavyweight champion Rocky Marciano heading to what Mayweather has said might be his final fight in September.

The victory was greeted by a chorus of boos from the crowd, indicating a belief he was by far the more active fighter. But Dave Moretti gave it to Mayweather 118-110, and Glenn Feldman and Bert Clements each favored Mayweather 116-112. Newsday's card saw a much different fight, 117-112 for Pacquiao.

The referee was Kenny Bayless, and the judges were Glenn Feldman, Bert Clements and Dave Moretti.

The fight originally was scheduled to take place in 2010, but it fell apart when Mayweather insisted the Pacquiao submit to random blood and urine testing. From that point forward, negotiations were fitful, contentious and unproductive, and when Pacquiao was knocked out by Juan Manuel Marquez in this same arena in December, 2012, it seemed the fight between the two most acclaimed fighters of their generation would not happen.

But Pacquiao, 36, regained his WBO welterweight title and won his past three fights, and with the sand running out of Mayweather's glass at the age of 38, he at long last agreed to a bout that he said likely will be followed by just one more in September. Ultimately, the delay stoked world-wide anticipation for a fight expected to generate record revenue of more than $300 million and purses approaching $180 million or more for Mayweather and $120 million for Pacquiao.

Pacquiao figured to pose problems for Mayweather with his hyper-speed punching and his unorthodox southpaw style. But Mayweather seemed emboldened by Pacquiao's knockout by Marquez, suggesting it might have rendered him more vulnerable to a repeat performance.

Floyd Mayweather Sr., who trains his son, went so far as to predict an easy night and a victory by KO. "I don't think it's going to be much of a fight," Floyd Sr. predicted. Referring to the Marquez KO, he added, "Once you get hit like that and go to sleep, it's going to happen again."

That prompted Pacquiao trainer Freddie to suggest Mayweather might deviate from his usual cautious, defensive style to try for a spectacular early knockout. But a long delay because of problems with the pay-per-view systems processing orders pushed back the start to 11:59 ET. Maybe it took the edge off the fighters who probed cautiously in the opening round with Mayweather landing a couple of quick rights.

In the second, Pacquiao succeeded in exerting more pressure and pushing Mayweather to ropes to land quick flurries, but it was a struggle to get past Mayweather's longer reach. Pacquiao adjusted in the third round, stepping right and planting and then coming back with the left inside Mayweather's jab. Often coming in low, he was placed in a headlock by Mayweather, who landed a sold right at the end.

Pacquiao found his rhythm in the fourth and had the crowd roaring as he drove Mayweather back with a straight left and followed with a flurry of power shots as Mayweather covered up. Twice more in the round, Pacquiao landed hard lead rights. In the fifth, Mayweather was far more cautious, landing an early right and taking one back later. No real advantage in that round.

The sixth was another big Pacquiao round, opening with a three-punch combo before a hard left set up a flurry of seven or eight Pacquiao power punches. Pacquiao ended the round with a hard right counter.

Mayweather opened the seventh with a solid right, but then got on his bike, moving away. Pacquiao cut him off expertly, continuing to move right and landed a couple effective combinations, starting with a straight right. In the eighth, Mayweather tagged Pacquiao a couple times, once a shot to the shoulder that Pacquiao shook off to show he wasn't hurt. But overall, it was a frustrating round for Pacquiao as Mayweather eluded him.

Even when Pacquiao wasn't scoring heavily in the ninth, he succeeding in pinning Mayweather in the corner or against the ropes for brief flurries. Mayweather tried to drop the right-hand bomb a few times and came close, but Pacquiao refused to be suckered into it. In the 10th, it seemed pacquiao was in clear control, not hurting Mayweather, but outpunching him.

Perhaps sensing the danger he was in, Mayweather came out aggressively with a right lead in the 11th and followed it up with several more hard right hands in the round. One wasn't exactly an uppercut but was rising when it caught Pacquiao on the chin, stunning him.

With his perfect record seemingly in the balance entering the 12th, Mayweather did nothing extraordinary to try and sway the judges. Maybe he assumed they were not crediting Pacquaio, who chased Mayweather around the ring at the end, popping shots as many in the crowd chanted his name.