The pair were familiar with each other having sparred hundreds of rounds when working under the same trainer in Shane McGuigan, something which aided Billam-Smith securing a majority-decision victory.
However, Okolie can only have himself to blame for losing his world crown and undefeated record having twice been deducted points for holding and being fortunate not to lose more.
Billam-Smith scored three knockdowns in the fight, the first and third being scored correctly but Okolie was harshly judged to have been felled by a punch with the second.
One judge incredibly scored it 112-112, but the others, albeit perhaps too wide at 116-107 and 115-108, deservedly had it in Billam-Smith's favour.
DOWN GOES OKOLIE! 😱 pic.twitter.com/DbsgRrQKlQ— Sky Sports Boxing (@SkySportsBoxing) May 27, 2023
Up until Okolie was floored in the fourth, it appeared that he would successfully negotiate the challenge of the hometown favourite, even if it came from excessive holding after the majority of his single shots and combinations.
Once Okolie was dropped with a left hook for the first time in his career, the momentum changed, and the referee repeatedly had to speak with the champion for infringements.
Points were taken in rounds five and seven, while Billam-Smith landed further knockdowns in rounds 10 and 11, the former highly dubious but perhaps understandable from the level of leaning that Okolie was doing at the time.
Okolie still had plenty of success, landing an array of hurtful head shots throughout the fight that would have made observers question while he insisted on fighting so negatively until he was at the point of no return.
To his credit, Okolie was gracious in defeat at the final bell, allowing Billam-Smith to have his moment in front of 15,000 fans in Bournemouth.