Buoyed by one of the great chins in boxing and a fearlessness that defies description, Guerrero out-toughed Berto for a unanimous decision Saturday at the Citizens Business Bank Arena in Ontario, California.
Guerrero knocked Berto down once in each of the first two rounds and pulled out a gnarly, nasty, gritty victory. All three judges had it 116-110, or eight rounds to four, in favor of Guerrero.
It wasn't so much that Guerrero beat Berto that was the shocker, though. Rather, it was the manner of the win. For most of the bout, it was like a street fight as they took turns teeing off on each other while standing inches apart.
Berto made himself look bad when he whined about referee Lou Moret, who had an extremely bad night but whose mistakes definitely did not cost Berto the win.
Regardless, Berto is a hard puncher and once he gathered his composure after he was blitzed the first two rounds, he raked Guerrero with some hard shots.
But Guerrero, a one-time super bantamweight who was fighting for just the third time above lightweight, kept coming for more.
"I did tell Andre I was going to beat him down, so I had to be a man of my word," Guerrero said, grinning.
Both of Berto's eyes were closed, as was Guerrero's right in a fight that was a throwback to the kind of battle the late Hall of Famer Carmen Basilio used to wage regularly a half decade earlier.
Neither man shied from the battle, though it was stunning that Guerrero could take such hard blows from a legitimate welterweight. He showed perhaps the best chin in boxing since Wayne McCullough, the Irish Olympian and former super bantamweight champion.
With only a slightly above average chin, Guerrero could not have won this fight.
"He didn't hurt me at all and I took some good shots from him," Guerrero said. "Halfway through the fight, he caught me with a shot on the eye and I couldn't really see. That's why I had to fight on the inside a lot more, too. He's a strong guy and he punched hard, but I've got a good chin and I was able to take the shots."
Moret let both men get away with questionable tactics. On the first knockdown, Guerrero had his right hand wrapped around the back of Berto's head as he hit him with a left. Berto, by contrast, was repeatedly winging hard shots at the back of Guerrero's head.
Guerrero sloughed the fouls off and kept fighting, while Berto seemed to lose his composure and began to moan to Moret.
After the fight, he was pretty much sour grapes while whining about Guerrero and Moret. He won a lot of fans by the way he fought, but he promptly lost a lot of them back after he failed to give Guerrero even a smidgen of credit.
"It was ridiculous," Berto said of Moret's work. "The referee kept calling me for a lot of different things. It made me timid to do a lot of things, throwing punches that I wanted to throw. He kept warning me for things that I didn't have no control over."
For the second year in a row, Berto participated in a Fight of the Year-type of bout. But he lost each of them and, at this point, is a spoiler in the division, a few clear steps behind the elite guys.
Guerrero, the guy who has been derided for calling out the likes of Floyd Mayweather Jr., Manny Pacquiao and others, showed Saturday he has a lot more going for him than perhaps many believe.
He's now squarely in the mix with the world's best welterweights.
And best thing of all, he just wants to fight.
It was a satisfying end to a roller coaster fight day. Hatton returned to the sport after more than 3 1/2 years in retirement. He sold 24,000 tickets in just 48 hours before the opponent was known, as fans in his native Manchester, England, welcomed him back to the sport like a conquering hero.
He fought well and was ahead of Vyacheslav Senchenko on all three cards when he was knocked out in the ninth by a hook to the ribs.
That was a downer that totally deflated the enormous, pro-Hatton crowd.
Keith Thurman showed in the opener of HBO's doubleheader that he is going to be in the mix for a lot of entertaining battles at super welterweight when he simply overran Carlos Quintana.
And then Guerrero and Berto capped the night with a barnburner.
It was clearly Guerrero's fight, but this was one of those bouts where there were no losers.
In boxing, the fans often take it in the shorts, but on this night, even the fans came out ahead.