The Sheffield-based fighter claimed the bout on a majority verdict, winning 117-111, 116-112 and 114-114.
Brook started off on the back foot and sustained a cut over his left eye early on, but grew in confidence as the fight progressed and eventually came away a comfortable winner, stunning Porter in front of his home crowd.
"You can tell how much this means to me. From a nine-year-old I've dreamed of being a world champion," said Brook, whose record improves to 33-0.
"I was born to do this. I always find a way - I always deliver.
"I've been dreaming about this moment since I was nine-years old. It's unbelievable.
"I was scrappy tonight, and not as slick as I wanted to be. But I'm the world champion now, baby. I was born to do this.
"I'm ready for a mega, mega fight next. I'll take on Keith Thurman or Floyd Mayweather. Amir Khan should get in queue now. I'm the world champion now so they're all going to want to fight me."
The result was a major shock for the world of boxing as Porter - who beat Devon Alexander and Paulie Malignaggi in his previous two fights - lost his crown, and Porter immediately asked for a re-match.
"I think I'm still the champion,'' he said. "I'm 24-1 and Team Porter will be back to the drawing board. There are no excuses. I do want the rematch."
How the fight progressed
The Stub Hub Centre was a subdued host to approximately 3,000 fight fans. Jimmy Lennon Jnr must have thought he was in the wrong place for a card which had three world titles on the line, and the main event was a fairly untidy affair from round one.
Making the second defence of his IBF title, Porter, 26, was keen to impose himself on the inside and score with body shots. Brook found his jab tricky to land due to good head movement from the American, who launched powerful hook-laden flurries. Brook landed with a right hand before the bell to gain his attention.
Brook started the second with a better jab, but was prone to hold on quickly when Porter was in close and couldn’t get any rhythm together. A large cut opened up above his left eye, caused from a clash of heads as Porter came in low.
At points during the early rounds, it looked like the physical strength of Porter coming forwards and his industry on the inside would prove to be too problematic for Brook, who couldn’t land cleanly with his lead punches. Single shots were not enough to keep the ‘Duracell Bunny’ away, but as the fight progressed, Porter’s attacks became ungainly and Brook started adapt and cope.
As the sixth got underway, Brook stood his ground, and while Porter answered back in kind, the cleaner work came from the challenger. Porter was now cut above the left eye from a head clash.
Brook’s progress was halted temporarily by a left hook halfway through the seventh, and he was forced to absorb a spirited but ugly attack from the American until he buzzed him with a right hand and followed up with eye catching shots to end the round.
Porter tried to steamroller in at the start of the eighth, while Brook continued with the front foot plan. His jabs provoked more aggressive flurries, which were crude and not scoring Porter enough clean hits to guarantee many of the later rounds.
As Brook’s confidence grew, he began to make Porter look one dimensional. When he returned to his corner at the close of the tenth, he was was in the driving seat and remained so in the eleventh and a scrappy closing round which was difficult to score for either.
Brook was immediately hoisted on the the shoulders of trainer Dominic Ingle for a victory lap. Porter looked despondent, as if he knew he hadn’t done enough down the stretch to keep his title.
BoxRec News scored a close 115-113 for Brook in a fight of two halves and expected the reverse to be the case. A draw wouldn’t have surprised. The judges tallied 114-114 (Dave Parris - UK) and 117-111 (Max DeLuca, US) and 116-112 (Adalaide Byrd, US) for Brook.
The two Americans put in questionably wide cards for Brook, perhaps appreciating his cleaner, more tasteful work. Afterwards, Porter mentioned the possibility of a rematch, but you wouldn’t want to watch this one again.
Brook has silenced doubters and is now in a powerful position in the welterweight division. Plans for a big fight with Khan in the UK will be now be drawn up.
- Sports & Recreation