British light heavyweight Buatsi secured a victory yet underwhelming debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a close 10-round bout at the boxing arena.
But the challenger landed significant shots, landing some telling individual punches in a match where the approaches never quite clicked, with constant grabbing disrupting the fight.
The scoring judges judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest showing but what defines champions? They win," Buatsi stated in the arena as he was faced disapproval from the audience.
The British fighter returned to winning ways after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers felt the challenger, 31, deserved the decision but the contender experienced the second defeat of his 28-bout professional journey.
The Champion Claims Triumph in Uneventful Encounter
The fighter's advancement has plateaued in recent times through contract problems and extended periods of inactivity.
Previously predicted as the next star of British boxing, he now stands trying to achieve expectations - possibly in what appears to be a final roll of the dice - under recent support.
He started carefully, with both competitors ready to be aggressive in a calculated initial rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after damaging his hand mid-fight, was competing in only his second fight at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a solid defense to barely take the better periods.
The spectators' acceptance decreased during frequent holding, with the challenger slipping to the canvas several times during grappling.
Parker finished the stronger, but several stanzas were hard to judge. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, awarding Buatsi just one round.
Buatsi progresses, but with the likes of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Hatton Homage Inspires Local Rivalry Fight
In the secondary fight, Lyndon Arthur beat Rea by close verdict in a excellent Manchester vs Manchester fight to secure the European light-heavyweight title.
The arena grew hushed for a extremely emotional tribute prior to the bout as ten bells sounded in remembrance of local hero Hatton, who died aged 46 in last month.
It was the first major televised match card in the location since Hatton's death. As the concluding sound ended, the quiet transitioned to a roar of "only one Ricky Hatton".
The competition during the bout matched the emotion. Arthur was floored by a powerful punch squarely on the chin in the second round, rising shakily to his position on the referee's count.
But the red-colored equipment of the fighter soon pressed ahead again. From the other corner, the opponent - in opposing blue - was marked up soon, significant bruising forming under his face as the fighters landed punishing blows.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity seldom decreased over twelve rounds.
The victor narrowly won the verdict with scoring tallies of 114-114, 115-113 and 115-112, but the two athletes were relentless and full of heart, all the qualities their idol the legend represented.
