Briton Joshua Buatsi outpointed friend and rival Dan Azeez in a brilliant all-British light-heavyweight encounter at Wembley's OVO Arena.
Buatsi floored his fellow Londoner twice in the 11th round, although Azeez insisted he slipped on both occasions.
Two judges scored it 116-110 and the other 117-109 to Buatsi in a bout where both men continued swinging into the final seconds.
"He pushed me every round, he's a champion," Buatsi, 30, said.
"I couldn't have done it without Dan, it's a pleasure to share the ring with him. Dan was pounding my head. He made me fight every second. Dan, big up yourself."
The contest was an eliminator for WBA champion Dmitry Bivol's world title, while Buatsi also picks up the British and Commonwealth belts with his 18th professional win.
Azeez, who suffered a first defeat in his 21st bout, was gracious in defeat.
Buatsi claims south London bragging rights
Buatsi and Azeez served up a domestic dust-up for the boxing purist.
In quite the striking visual, Azeez made his ring walk second and headed straight to the middle of the ring to meet Buatsi face on. He skipped on the spot as Buatsi shadowboxed - neither man averting their gaze.
They have sparred hundreds of rounds together but it was an altogether different proposition competing with smaller gloves and under the bright lights of the arena and a vocal crowd - with allegiances seemingly split between the south Londoners.
Buatsi found early success to the body but was susceptible to the counter. The fight really came alive in the third as both men stood in the centre and traded.
The fifth was even better as they landed thunderous punches, showing both their desire to win and durability.
With high-worn velvet shorts and pulled up socks, Azeez is a throwback fighter who has modelled himself on his boxing hero and middleweight great Marvin Hagler.
He was having success up until the midway stage but the more eye-catching punches and higher output was coming from Buatsi.
Azeez's back leg gave way in the eighth and Buatsi pounced, landing with a body shot. In a bizarre moment, Azeez's corner then threw the towel into the ring in between rounds.
With the referee almost extending his arms to call off the contest, the corner anxiously told him to use it to wipe sweat off the canvas.
The ring resembled an ice rink at times with both fighters losing footing. In a dramatic 11th, Buatsi threw a right hook as Azeez simultaneously appeared to slip.
Azeez rose to his feet but moments later he was on the floor again courtesy of another right hook. Again, Azeez protested to the referee it was a slip.
Buatsi will have known he was ahead on the cards in the final round but it did not deter him from finishing in style as he continued to trade until the final bell.
He is now in line to face Bivol but may have to wait for his shot. The Russian is likely to contest an undisputed title fight with fellow champion and compatriot Artur Beterbiev this summer.
Azeez can lift his head high despite suffering a huge blow to his immediate world-title hopes. A latecomer to the sport who turned pro just over six years ago, he still has a bright future in the sport.
BBC