Rossi needed medical attention and took a long time to get up after Huck left the 30-year-old left-hander sprawled on the canvas with a clean right punch.

The 26-year-old Huck, 34-1 with 25th knockouts, also knocked Rossi down in the third round, and was penalized two points for flooring him again well after the bell at the end of the fourth round.

"I think I hit him after the bell," Huck said, prompting a mixed response from the home crowd.

With Rossi still clearly feeling the effect, Huck went for the knockout in the fifth, when he twice brought the challenger down again, before finishing him off in the sixth.

"I had 12 rounds and probably took too much time," Huck said. "Maybe I could have ended the fight earlier." Rossi, penalized a point for low punches in the third, dropped to 17-3-1 with his first loss since 2007.

"I asked him if he wanted to stay in the corner but he likes fighting and he decided to fight on," Rossi's coach, Luis Barrera, explained after the Argentine came out for the fifth round.