UK light heavyweight Buatsi made a winning yet disappointing beginning to life under new promoters with a points victory over Zach Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a competitive ten-round fight at the Manchester venue.
But the challenger landed significant shots, delivering effective single shots in a match where the techniques never quite clicked, with frequent clinching spoiling the action.
The scoring judges scored it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my greatest performance but how do champions respond? They win," the victor said in the ring as he was faced disapproval from the crowd.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Various analysts thought Parker, thirty-one, deserved the victory but the contender experienced the second loss of his 28-bout professional journey.
The Champion Claims Victory in Slow Match
The fighter's advancement has plateaued in recent years through management issues and extended periods of inactivity.
Previously predicted as the future of British boxing, he now is positioned trying to achieve expectations - maybe in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors ready to overcommit in a tentative initial rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand during the bout, was participating in his second fight at the higher weight class.
By the halfway stage, Parker had stayed in contention, creating difficulties for Buatsi, who worked behind a solid defense to barely take the more effective periods.
The crowd's patience diminished because of regular grabbing, with Parker slipping to the canvas various instances during grappling.
Parker finished the stronger, but several stanzas were hard to judge. Nevertheless, previous titleholder Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the presence of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Tribute Fuels Manchester Derby Battle
In the supporting bout, Arthur overcame Rea by close verdict in a outstanding Manchester vs Manchester fight to win the European light heavyweight belt.
The venue grew hushed for a profoundly moving memorial ahead of the contest as 10 bells rang in honor of the city's native Ricky Hatton, who succumbed aged 46 in last month.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the concluding sound disappeared, the silence gave way to a chant of "there's just one Hatton".
The competition inside the ropes matched the emotion. The eventual winner was knocked down by a powerful punch flush on the face in the second round, standing uncertainly to his feet on the eight count.
But the red-colored shorts of the fighter soon advanced again. Across the ring, Rea - in opposing blue - was injured early, heavy swelling developing under his orbital area as the duo landed punishing blows.
The challenger, 27, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the action rarely dropped over 12 rounds.
Arthur narrowly won the verdict with scoring tallies of draw, narrow lead and 115-112, but both fighters were relentless and full of heart, exactly what their idol Hatton represented.
