Kelly Pavlik claimed the undisputed world middleweight crown with a seventh-round stoppage of fellow American Jermain Taylor on Saturday.
Kelly Pavlik goes toe-to-toe with Jermain Taylor
Pavlik, 25, who recovered after being floored by Taylor in round two, unleashed a flurry of punches to leave the champion slumped in the corner.
Taylor, 28, was making a fifth defence of the title he took from Bernard Hopkins in July 2005.
But Pavlik was too strong in Atlantic City and carried off the WBC/WBO belts.
Big-punching Pavlik, from Youngstown, Ohio, was happy to trade punches in a thrilling toe-to-toe encounter in Boardwalk Hall.
Taylor was far more offensive then in his previous defences against southpaws Kassim Ouma and Cory Spinks, which sparked a thrilling spectacle from the first bell that often had the crowd on its feet.
With Pavlik parading a perfect 31-0 record and Taylor also unbeaten at 27-0-1, something had to give.
I just can't believe I lost. I had him hurt and I thought I had him.
It was the champion who landed the first major blow of the fight in the second round as he sent the challenger to the floor with a blaze of punches.
Pavlik took the mandatory count from referee Steve Smoger but still looked out of it as Taylor went back in to finish his man off. But somehow, Pavlik managed to stay upright and hang on and in the third round he came powering back into the fight.
He was finding plenty of success with his jab, picking off Taylor almost at will as he moved the champion around the ring.
But it was a stunning power punch that sent Taylor reeling back into Pavlik's corner midway through the seventh.
Pavlik again sent a left jab through the Taylor defences before delivering a crunching right that sent Taylor back-pedalling into the corner.
Pavlik went straight after him continuing the assault with a stunning series of punches, a right upper-cut to Taylor's chin followed by a clubbing left hook and then another left that had his man sinking to the floor and out of the fight.
"I just can't believe I lost," Taylor said. "I had him hurt and I thought I had him.
Pavlik celebrates his stunning win over Taylor
"I wasted a lot of energy by throwing unnecessary punches that I shouldn't have. I got caught."
There is a rematch clause in the contract and both fighters said they would honour the agreement.
"I would like to fight him in my very next fight," Taylor said. "I have to go back to the drawing board."
Pavlik said: "He caught me flush early on to put me down but I showed heart.
"Once I got up and shook off the cobwebs, I knew it would be a good night. I got up because I didn't get hit as hard. I hit him with a lot of flush shots. It caught up to him."