Joe Calzaghe battled back from a stunning first round knockdown to score a disputed split decision victory over Bernard Hopkins in Las Vegas and reign as light-heavyweight world number one.
Calzaghe extended his unbeaten record to 45 fights but only after by far the toughest test of his career against 43-year-old Hopkins, whose big right hand had got him off to a flying start.
But the brilliant Welshman fought back strongly in the second half of a fight which was marked by frantic exchanges and touched by controversy when Hopkins claimed a low blow in round 10.
Judge Adalaide Byrd thought Hopkins had done enough to edge a 114-113 verdict but Chuck Giampa (116-111) and Ted Gimza (115-112) both scored in favour of Calzaghe's excellent second half of the fight.
Calzaghe said: "I fought really hard tonight. As the fight wore on I had to really let my punches go. He was very defensive. A win is a win. I was only hurt once and he never caught me with a clean punch.
"That knockdown was a slip but it was one of the toughest fights of my career. I'm very proud to have been the one to have landed the most punches on Hopkins in his career.
"It wasn't pretty and it wasn't my best night but I know I won. It's my second world title in a second division and I am in America. It is the icing on the cake for my career."
Calzaghe's win gave him the Ring magazine's version of the 175lbs title to add to the undisputed super-middleweight crown he still owns. And it will also bring him the global recognition he claims.
But he had to work for that recognition. Watched by A-list celebrities including Sylvester Stallone and Arnold Schwarzenegger, Calzaghe made a nightmare start and was dumped to the canvas straight away.
The Welshman was quickly back on his feet to receive the mandatory eight count from referee Joe Cortez but his propensity to ship right hands was alarming and he caught another big right which cut the bridge of his nose.
Calzaghe enjoyed his first moment of success in the second when he clattered home a wide left hook but rock-hard Hopkins shrugged off the shot and fired back with a strong right uppercut.
Hopkins' bullish style was skirting the edge of the rules but it was Calzaghe who was warned by Cortez towards the end of the second for an apparent low blow which temporarily stopped the American in his tracks.
Hopkins stayed on top, digging a right hand into Calzaghe's body early in the third, but there were signs the Welshman was finding his distance better and finding a few more moments of success with his left.
Calzaghe began unloading towards the end of a third, banging home a fine right hand as the American was backed against the ropes, but Hopkins again responded with rights to the body before the bell.
Both fighters were warned after a scrappy opening to the fourth but Calzaghe seemed to be slowly getting to grips with his rival, making him miss with rights and landing a couple of flush lefts in the frantic exchanges.
It was arguably Calzaghe's first round on the cards, and he continued to avoid Hopkins' best shots in a tight fourth which carried on briefly after the bell after both men looked to unload.
Approaching the halfway mark, Calzaghe scored a super straight left through the middle as the 43-year-old began to blow, but Hopkins was still a real danger, landing a nice left hook.
Again the round ended chaotically with Calzaghe wrestled onto the canvas after a frantic exchange. Cortez rightly ruled no knockdown, but Hopkins was undoubtedly ahead after six.
A big left hook from Calzaghe was his cleanest work of round seven, but Hopkins wobbled the Welshman from another jarring right on the bell.
Calzaghe had the better of round eight, jolting home two lefts and finishing the round strongly. He was catching his rival on the cards but Hopkins did not seem in the least bit troubled by the Welshman's power.
Constantly circling away from Hopkins' right hands and nipping swiftly in and out, Calzaghe continued to enjoy success with the left in the ninth, a hook whipping home as he continued to dredge the fight back towards parity.
Hopkins slumped to the canvas early in the ninth claiming a low blow, much to the fury of Calzaghe, whose case appeared to be supported by video replays which showed only the slightest of connections.
When the action resumed two minutes later Hopkins, suitably refreshed, landed a fine right but Calzaghe was soon back in his rhythm, giving as good as he got up close and ending the round well.
Hopkins tried to take another breather in the 11th but was ordered to fight on by Cortez, sparking a furious assault by Calzaghe who slammed home a big right and seemed to hurt Hopkins for the first time.
The stage was set for a furious final round and Calzaghe started well, drilling a left through the middle while Hopkins banked on the powerful right counter-shots which had been serving him so well.
Both fighters raised their arms in victory before the final bell but after 12 furious rounds the action was far too close to call with any degree of certainty.
Clearly Calzaghe - who landed 33% of his shots as opposed to 27% for Hopkins - had been rewarded for his accuracy although Hopkins left the ring fuming at the verdict.
"I controlled the pace like a true veteran. I never got hurt in the fight. I never got hit with any big shots. I have nothing to be ashamed of," he said.
"One thing about boxing, the fans are the judges. They can't be fooled. They have seen a 43-year-old throwback take this guy to school and make him look an amateur."