UK light heavyweight Buatsi earned a win yet underwhelming start to his career under new promoters with a decision win over Zach Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger had his moments, landing some telling single shots in a contest where the approaches never quite clicked, with frequent clinching disrupting the fight.
Two judges had it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest display but what defines champions? They succeed," the victor said in the arena as he was faced negative reactions from the audience.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in February - to earn a 20th career victory.
Various analysts felt the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter endured the second defeat of his 28-fight professional journey.
Buatsi Secures Triumph in Dull Match
The fighter's advancement has plateaued in the past few years through management issues and long spells of lack of fights.
Previously predicted as the next star of British boxing, he now finds himself trying to achieve expectations - possibly in what feels like a last chance - under recent support.
He began cautiously, with both competitors ready to be aggressive in a cagey initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in 2022 after breaking his hand in the contest, was making just his second fight at light-heavyweight.
By the middle rounds, Parker had kept it close, causing problems for Buatsi, who utilized a protective stance to narrowly win the more effective periods.
The spectators' acceptance decreased amid constant clinching, with Parker going down several times during clinches.
The underdog ended stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor advances, but with the likes of power puncher David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Hatton Memorial Motivates All-Manchester Contest
In the supporting bout, Arthur beat Rea by close verdict in a terrific all-Manchester fight to win the European light heavyweight title.
The stadium grew hushed for a deeply poignant memorial before the fight as 10 bells sounded in honor of Manchester's own Hatton, who died 46 years old in September.
It was the premier televised match card in the city since Hatton's death. As the final chime ended, the quiet gave way to a shout of "there's just one Ricky Hatton".
The competition within the ring equaled the feeling. Arthur was floored by a significant blow directly to the jaw in the second round, getting up unsteadily to his footing on the eight count.
But the red-colored equipment of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was injured quickly, heavy swelling developing under his face as the fighters exchanged powerful shots.
Rea, twenty-seven, landed power punches but the champion, 34, responded in kind with stinging uppercuts as the intensity seldom decreased over 12 rounds.
Arthur edged the result with judges scorecards of even score, 115-113 and wider gap, but the two athletes were determined and courageous, exactly what their hero Hatton represented.
