The news conference afterward was filled with the usual congratulations for the winners and talk about bigger things to come. Oscar De La Hoya was the promoter and he answered questions in two languages, thanked all for coming and declared the night a success.
Outside, HBO was hosting a poolside party at the MGM Grand hotel-casino for those lucky enough to get an invite. There was plenty of food, drink and laughter for the fight crowd.
Spirits weren't so high in a hospital not far from the glittering Las Vegas Strip. There, Leavander Johnson lay in a coma in the intensive care unit, his doctor unsure he would survive the night.
This was the dark side of boxing, the one that fans who pay US$500 to sit ringside never see.
Johnson had hoped to end the biggest night of his boxing life with the IBF lightweight title belt still around his waist. He might have even enjoyed himself at the HBO party afterward.
Instead, he was in a deep coma that doctors induced to try to save his life.
"He was fighting for a world title, then a few minutes later here he is fighting for his life," said Johnson's father, Bill, who also is his trainer.
Johnson said his son knew the risks. He had been fighting for money for 16 years, and understood that taking punches to the head could be dangerous.
Unfortunately, as Mike Tyson likes to say, boxing is a hurt business.
But it shouldn't hurt this bad.
Johnson left the ring upright, not knowing that a blood clot was beginning to form that swelled so big it moved his brain from the right side of his skull to the left. When his left leg began dragging on the way to the dressing room, though, it was clear something was terribly wrong.
The doctors of the Nevada Athletic Commission saw it and acted quickly.
In the space of 40 minutes, they got him to the hospital and then into surgery. A surgeon took out a piece of his skull to get in, then left it open so his brain would have room to swell.
Johnson may live, though it's too early to tell. The problem is, his injury is not an isolated one.
Four times in the last four months in Las Vegas, boxers have left the ring bleeding in the brain. One is dead, while two others survived.
It's scary, but also puzzling. It might be a statistical anomaly, but doctors can't say. They just don't know enough about why some fighters are injured while others can spend a career getting hit in the head and show no ill effects.
The only thing they're sure of is it isn't something in the water.
"That is the biggest concern of all, that there have been so many of these," said Dr. Margaret Goodman, a neurologist and the ringside doctor who examined Johnson during the fight. "I think we need to evaluate the system from top to bottom."
What is clear is that Johnson took a savage beating in a fight that probably shouldn't have gone as far as it did, 38 seconds into the 11th round.
The 35-year-old fighter spent 16 years chasing a title, and finally won one on an upset in Italy in June. His reward was a US$150,000 payday to defend his title on a card that included fighters with pedigrees such as Shane Mosley and Marco Antonio Barrera.
He fought valiantly, but was outclassed by Jesus Chavez, who rarely missed with punches that were thrown with bad intentions. Bill Johnson warned his son at one point he was going to stop the fight, but it continued into the 11th round when Chavez threw some two dozen unanswered punches and referee Tony Weeks finally stopped it.