British light heavyweight Buatsi earned a win yet underwhelming beginning to his career under recent management with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's activity level likely gained him a majority decision in a tight 10-round fight at the boxing arena.
But Parker landed significant shots, delivering effective individual punches in a fight where the approaches failed to mesh, with excessive holding disrupting the action.
The officials judged it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my best display but what defines champions? They succeed," Buatsi said in the ring as he was met by disapproval from the spectators.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to secure a 20th pro success.
Several boxing experts felt Parker, 31, merited the win but the British boxer endured the second defeat of his 28-bout professional journey.
The Champion Claims Win in Slow Match
The fighter's advancement has stalled in the past few years through contract problems and long spells of lack of fights.
Earlier forecast as the rising talent of British boxing, he now is positioned trying to realize his potential - maybe in what feels like a ultimate opportunity - under recent support.
He started carefully, with neither fighter prepared to take risks in a calculated early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for Buatsi, who operated with a solid defense to edge the more effective stanzas.
The audience's tolerance wore thin amid regular grabbing, with Parker slipping to the canvas several times during clinches.
Parker finished the stronger, but several stanzas were challenging to assess. However, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still appears challenging.
Hatton Memorial Fuels Manchester Derby Fight
In the supporting bout, Arthur defeated Rea by divided decision in a outstanding Manchester vs Manchester battle to capture the European light heavyweight championship.
The venue became quiet for a extremely emotional homage before the fight as ten bells sounded in remembrance of Manchester's own Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast match card in the city since the passing of Hatton. As the final chime ended, the stillness transitioned to a roar of "only one Hatton".
The fighting inside the ropes matched the sentiment. The eventual winner was knocked down by a left hook directly to the face in the early round, getting up unsteadily to his footing on the eight count.
But the traditional red equipment of Arthur soon came forward again. From the other corner, the opponent - in competitive blue - was injured early, heavy swelling developing under his face as the fighters landed punishing blows.
Rea, 27, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the action seldom decreased over 12 rounds.
Arthur barely secured the result with scoring tallies of 114-114, 115-113 and 115-112, but the two athletes were determined and full of heart, all the qualities their idol the legend represented.
