It was Bradley's first fight since losing for the first time in his professional career against
It was a surprising decision because Bradley repeatedly landed rights against Chaves and eluded most of Chaves' clean blows.
Bradley said he thought he had won eight rounds.
Julie Lederman scored it 116-112 for Chaves, Burt Clements had it 115-113 for Bradley and Craig Metcalfe had it 114-114.
The Chaves-Bradley decision wasn't the only surprising one of the night.
Jose Benavidez (22-0) won a unanimous decision over Mauricio Herrera (21-5) to claim his interim World Boxing Assn. super-lightweight belt. But many in the crowd believed Herrera had won the fight.
Andy Lee (34-1) shocked previously undefeated Matt Korobov (24-1) with a technical knockout with 1 minute 10 seconds left in the sixth round.
"Julie Lederman should not be judging fights," promoter Bob Arum said.
Arum said he thought Bradley handily won eight of the 12 rounds. Arum said he was fed up with the judges and felt there were not enough quality judges available for two major fight cards in Las Vegas on the same night.
Golden Boy Promotions also had a card at the MGM Grand.
But Chaves felt good about the decision.
"I think it was an even fight, but I thought I was superior," Chaves said.
The fight had multiple head butts. Bradley's left cheek was badly swollen from some of those head butts and from Chaves' rights to the face.