Ricky Hatton survived arguably the toughest fight of his career against Luis Collazo at the Boston Garden to be crowned the WBA welterweight champion.
Hatton puts Collazo on the deck inside the first 10 seconds
In his first fight at the higher limit, the former light welterweight king floored his tricky southpaw rival in the first 15 seconds of the contest.
But American Collazo pushed Hatton all the way before losing on points.
Hatton was ahead on all three cards - 115-112, 115-112, 114-113 - as he became a two-weight world champion.
The victory also took his fight record to 41 wins, with 30 KOs. Collazo, 25, has now lost twice in his 28-bout career.
Hatton lived up to his billing as the bookmakers' favourite when he sent Collazo stumbling to the canvas early on.
But after dominating two rounds the Briton was steadily pegged back and troubled by the more experienced welterweight.
The 27-year-old from Manchester struggled throughout to find his range at the heavier weight and rarely punished Collazo with his usual array of body shots.
He did at least boast arguably the greater work-rate, while Collazo's punches proved more venomous as the fight reached its final stages.
The American came within a whisker of a knockdown with a blistering combination of hooks in the final round but Hatton just managed to stay on his feet.
After the final bell, both men celebrated victory before Hatton was unanimously awarded the win.
"I was absolutely positive I'd won it at the end," said Hatton. "Every round was close or competitive but I felt I had the edge.
"Knocking him down that early was probably the worst thing I could have done because I went in to finish him.
"I had a rush of blood to the head and he was very clever and he knew how to look after himself.
"But every time I was under pressure and he was getting in control, I upped the tempo and pulled away again.
"It was maybe the toughest fight of my career because he was tough and attacking and cagey. In fact, he was a lot harder than I thought he would be.
"He's a good fighter and it certainly wasn't comfortable but I felt when I needed to up it, I did so."
Hatton hinted he could return to a lighter division.
But he added: "At the moment, all the best fighters are at welterweight - the Floyd Mayweathers of the world for example."
Collazo called for an immediate rematch in England, saying: "Hatton was out on his feet in the 12th.
"I thought I out-boxed him and was stronger. I thought a guy had to do more than he did to take my title."
Hatton did not rule out another clash with Collazo, saying: "I'll fight absolutely anybody and that includes a rematch with Luis.
"It's up to the teams to get together and do it. Yeah, why not? He hurt me several times in the fight. I'm man enough to admit it."
But he felt he would only improve at the higher weight limit.
"It's a good test at a new weight," he said. "I need to grow into this new weight. This was my first fight at 147 pounds and it was a title fight. I'll get better."
Prior to the fight, a moment of silence was observed by the crowd for former heavyweight champion Floyd Patterson, who died on Thursday at the age of 71.