LAS VEGAS – We’ve become so accustomed to watching Floyd Mayweather Jr. dominate his opponents that we’re shocked when one puts up any resistance.

That was the case on Saturday night at the MGM Grand, where a determined Miguel Cotto surprised many experts and fans by giving the undefeated boxing wizard a run for his money in an entertaining fight.

Mayweather won a lopsided decision to take Cotto’s WBA junior middleweight title: 117-111, 117-111 and 118-110 on the official scorecards. THE RING had 116-112, or eight rounds to four.

Don’t be fooled, though. This was no wipe out.

Mayweather (43-0, 26 knockouts) was at least near his defensive best, slipping or blocking most of Cotto’s punches. The Puerto Rican landed 21 percent of his shots, according to CompuBox. (Mayweather landed 26 percent.)

But Cotto, calm and confident from beginning to end, never stopped pressing the action. And when you do that, some of your punches will get through even against the best defensive fighter of his generation. Mayweather’s bloody nose was evidence of that.

And while Mayweather slipped in a nice variety of shots – some very hard – amid Cotto’s attacks, the fighters seemed to fight on roughly even terms most of the way.

That made a lot of the rounds difficult to score – some on press row had it a close fight – and kept pro-Cotto fans involved. More than once, many among the 16,047 that packed arena chanted “COTTO, COTTO, COTTO,” a sure sign that we had a competitive fight.

Mayweather almost took it out of the judges hands in the 12^thand final round, buckling Cotto’s knees a couple of times, but the brave champion finished in an appropriate position after his performance: on his feet.

Cotto (37-3, 30 KOs) lost a fight but gave Mayweather his toughest challenge since he narrowly outpointed Oscar De La Hoya in 2007 even though many wrote Cotto off after Antonio Margarito handed him a terrible beating in 2008 and Manny Pacquiao dominated him the following year.

Ricky Hatton, Juan Manuel Marquez, Shane Mosley and Victor Ortiz couldn’t cope with Mayweather’s skills. Cotto proved he could and made Mayweather dig deep in spite the scores.

It wasn’t so much old age that began to creep up on the 35-year-old Mayweather; it was a capable, gritty opponent who came to win.

Cotto probably did more in defeat to Mayweather to enhance his reputation than any recent victory. To say he remains an elite – and important – fighter is an understatement.

“The judges said that I lost the fight,” Cotto said. “… I have to take my defeat. I brought my best, and I did my best every morning in the training camp. I did my best tonight.

“He knows what kind of fight Miguel Cotto brings, and so do the fans. I’m happy with my performance and so is my family. I can’t ask for anything else.”

Meanwhile, the fact we’re surprised that Mayweather had to work to remain unbeaten says a lot about him. We see him as untouchable. To be reminded that he’s human after all was odd.

Mayweather obviously isn’t unbeatable but proved he can win even a competitive fight handily. He also had to prove he was both a boxer and a fighter on this night, which will enhance his legacy.

“I had to execute the game plan and fight my heart out,” Mayweather said.

Next on Mayweather’s schedule is a trip to jail on June 1, the first day of his 90-day sentence for domestic violence.

Mayweather seemed to be unfazed by that prospect immediately after his victory on Saturday, saying “I’m going to accept it as a true man would do.” And he is already discussing a potential next opponent who we know well: Manny Pacquiao.

Mayweather and Pacquiao have failed more than once to make the blockbuster fight but they probably will try again if Pacquiao beats Tim Bradley on June 9 at the MGM Grand.

Once again, that’s the fight the world wants to see. And somehow, perhaps because Mayweather will now be perceived as at least somewhat more vulnerable, that fight just became a little more interesting.

Photos / Naoki Fukuda

Follow Michael Rosenthal on Twitter @MichalRosenthal