Teofimo Lopez emerged victorious in a showdown against the previously unbeaten Josh Taylor, securing the World Boxing Organization light-welterweight title with a resounding unanimous decision.
Judges handed the 25-year-old Brooklyn fighter the victory by scores of 115-113, 115-113 and 117-111.
Lopez improved to 19-1 while dropping the 32-year-old Scottish southpaw, the former undisputed world champion in the division, to the same record.
Lopez, a former world lightweight champion, became a two-division world champion with the 140-pound crown.
"I'm so thankful. It has been a long time coming," Lopez said. "We just beat the number one guy, former undisputed world champion. It was about doing what I needed to do."
Lopez apologized to Taylor for saying in the run-up to the fight that he wanted to kill the Scotsman.
"He's a tough dude," Lopez said. "I can see why he beat so many fighters. You've got to counter a counter puncher."
Taylor has been the undisputed world light-welterweight champion after a controversial split-decision victory over England's Jack Catterall.
He dropped three of his titles to pursue a rematch with Catterall but Taylor suffered a foot injury that scrapped the planned bout.
That created a 16-month layoff ahead of the Lopez fight but Taylor said that was not a factor.
"The layoff had nothing to do with it," Taylor said. "I've got no excuses. He was better on the night.
"Wasn't my best. I thought it was a close fight. I know I can beat him."
Lopez went to the canvas in the second round and Taylor went down in the third on what were ruled slips by referee Michael Griffin.
Taylor struck Lopez with a jab in touching up the gloves on a restart in round two, when he was also warned about pulling down the head of the smaller Lopez.
A left uppercut by Lopez in the fifth round sparked cheers from hometown supporters but Taylor answered later with a hard left.
Lopez suffered a cut on the outside of his right eye but began pressing the attack in the middle rounds, hammering Taylor with a right to the head in the seventh and connecting with a lunging left as he leaped off the canvas late in the eighth round.
A right uppercut set up a double right combination for Lopez in the ninth and after dominating the 11th round, Lopez raised his arms in victory with another round to come, one that also went Lopez's way.