British light heavyweight Buatsi secured a victory yet underwhelming start to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a competitive 10-round bout at the Manchester venue.
But Parker had his moments, connecting with powerful individual punches in a fight where the approaches never quite clicked, with excessive holding disrupting the contest.
Two judges scored it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my greatest performance but what do champions do? They succeed," Buatsi commented in the ring as he was met by boos from the spectators.
The British fighter got back to winning after his first professional defeat - an memorable fight with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts thought Parker, thirty-one, should have been awarded the win but the contender endured the second setback of his 28-bout professional journey.
Buatsi Claims Triumph in Uneventful Encounter
Buatsi's progress has plateaued in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to realize his potential - perhaps in what feels like a final roll of the dice - under recent support.
He began cautiously, with neither fighter prepared to be aggressive in a tentative early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in 2022 after damaging his hand during the bout, was making just his second bout at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a solid defense to edge the cleaner periods.
The crowd's patience wore thin amid constant clinching, with the challenger falling to the floor multiple occasions during grappling.
Parker finished the stronger, but multiple periods were difficult to score. Although, former world champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor advances, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Homage Motivates Local Rivalry Fight
In the supporting bout, Arthur beat Rea by close verdict in a excellent local rivalry contest to capture the European light heavyweight title.
The venue grew hushed for a deeply poignant homage ahead of the contest as ten bells rang in memory of the city's native Ricky Hatton, who succumbed at age 46 in September.
It was the premier televised fight night in the urban center since the passing of Hatton. As the concluding sound ended, the stillness transitioned to a shout of "there's only one Hatton".
The fighting inside the ropes equaled the emotion. The eventual winner was sent to the canvas by a left hook flush on the face in the early round, getting up unsteadily to his footing on the eight count.
But the red-colored attire of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was injured early, noticeable damage forming under his eye as the duo landed punishing blows.
Rea, twenty-seven, landed power punches but the champion, 34, matched the intensity with powerful upward punches as the intensity hardly diminished over the full distance.
Arthur barely secured the decision with scoring tallies of 114-114, 115-113 and 115-112, but the two athletes were persistent and brave, everything their idol the legend embodied.
