Billy Joe Saunders beat Chris Eubank Jr on a split decision at London's Excel arena to retain his British, European and Commonwealth titles.
Saunders, 25, demonstrated his superior boxing skills to build a healthy lead against his less experienced opponent. But Eubank Jr, also 25, came on strong in the second half of the fight and had the champion in trouble at times.
Two judges scored the fight for Saunders - 115-114 and 115-113 - and the third 116-113 for Eubank Jr.
Former Olympian Saunders, who is now undefeated in 21 pro fights, is next expected to challenge for the WBO title, which will be contested by Ireland's Andy Lee and Russia's Matt Korobov on 13 December. Eubank Jr, who drops to 18 wins and one defeat, must bide his time before possibly earning a lucrative rematch a couple of years down the line.
Saunders said: "He had a good work-rate but it was a bit too slow in the early rounds. I'm ready for a world title. And when I get the world title, I'll give him the first shot."
Eubank Jr felt he had won the fight but acknowledged Saunders showed he had "a good engine".
He said: "It was a close fight. He did what I thought he would do. He boxed to plan in the early rounds but then I thought I overtook him. But I'll be back."
Chris Eubank Sr leads his son out of the ring after the fight.
The Brighton fighter, whose father was a two-weight world champion in the 1990s, had never been in a competitive fight before, winning 13 times inside the distance.
But Eubank Sr likened to his son to the great Sugar Ray Leonard during the build-up, while he was also said to have impressed in sparring against Nottingham's super-middleweight world champion Carl Froch.
Meanwhile, some suspected Saunders had taken the challenger lightly, although that looked far from being the case in the opening round, during which the champion landed with right jabs at will.
Saunders, from Hatfield, also had the better of the second round, making the challenger, who was struggling to come to terms with the champion's southpaw stance, look ungainly at times. Saunders probably nicked the third as well, despite Eubank Jr managing to land with a clunking left hook just before the bell, and the champion continued to outwork the challenger in the fourth.
Eubank Jr started the fifth round talking to Saunders but soon abandoned that tactic when his opponent, undeterred, continued to plough forward.
Eubank Jr managed to draw Saunders into some rugged exchanges in the sixth, but the champion probably won that round as well.
However, the tide began to turn in the seventh, with Eubank Jr showing more urgency, landing with a couple of hurtful right uppercuts and reddening Saunders around the nose and eyes. And Saunders showed definite signs of tiring in a sometimes desperate eighth, in which the challenger landed with one mind-scrambling right cross in particular.
Billy Joe Saunders bests bitter rival Chris Eubank Jr in British barnstormerEubank Jr, who had never gone further than eight rounds before, started the ninth like a train, pounding Saunders on the ropes and standing the champion up with a tremendous left hook towards the end of the round.
Saunders still appeared to hold a comfortable lead heading into the 10th but by the end of the round he looked just about ready to drop, having been assailed by a fusillade of left jabs and hooks. Eubank Jr, sensing his rival was wilting, continued to come bullocking forward in the penultimate round but Saunders continued to stand up to his best shots.
The 12th and final round was furious and sometimes brutal but when the final bell sounded most observers were of the opinion Eubank Jr had done too little too late.
Frankie Gavin, England's only ever amateur world champion, retained his British welterweight title and secured the Commonwealth belt with a contentious points victory over Londoner Bradley Skeete. Skeete, who was unbeaten in 18 pro contests before the fight, appeared to land the cleaner punches throughout but the judges scored it 116-112, 116-113, 116-113, all in Gavin's favour. Birmingham's Gavin, 29, now has 21 wins from 22 pro fights and remains on course for a world title shot.
Meanwhile, Norfolk's Liam Walsh added the British super-featherweight title to the Commonwealth belt he already owned with a unanimous decision over Yorkshire's Gary Sykes.