Buatsi had early success with the body, but was susceptible to counters. The fight really came to life in the third round as both men stood in the middle and traded trades.
The fifth time was even better, with a thunderous punch that showed both his will to win and his durability.
Dressed in frayed velvet shorts and pulled-up socks, Azeez is an old-school fighter modeled after boxing hero and middleweight great Marvin Hagler.
Things were going well until the middle stages, but Buatsi had the more eye-catching punches and higher output.
In the 8th inning, Azeez's back leg gave way and Bouatsi jumped and landed a body shot. In a bizarre moment, a towel was thrown into the ring on Azeez's corner kick during the round.
When the referee almost reached out to stop the fight, his corner anxiously instructed him to use it to wipe the sweat from the canvas.
The ring resembled an ice rink at times, with both fighters losing their footing. In the dramatic 11th round, Bouatsi landed his right hook just as Azeez was about to slip.
Azeez got back to his feet, but shortly after was hit with another right hook that sent him to the floor again. Once again, Azeez protested to the referee, saying it was a mistake.
Bouatsi would have known he had the advantage on the card in the final round, but that didn't prevent him from finishing in style, continuing to trade until the final bell.
He is currently in line to face Bivol, but may have to wait for his shot. The Russian will face fellow champion and compatriot Artur Beterbiev in an undisputed title fight this summer.
Azeez can be proud despite dealing a huge blow to his immediate world title hopes. Although he's a latecomer to the sport, turning professional just over six years ago, he still has a bright future in the sport.