British light heavyweight Buatsi made a winning yet disappointing debut to life under new promoters with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a split decision in a tight 10-round fight at the Co-op Live Arena.
But the challenger found success, delivering effective single shots in a contest where the approaches never quite clicked, with constant grabbing marring the contest.
The officials judged it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my greatest display but how do champions respond? They win," Buatsi commented in the ringside as he was met by negative reactions from the crowd.
The Londoner bounced back after his initial pro loss - an thrilling contest with Callum Smith in February - to claim a 20th pro success.
Various analysts felt the challenger, 31, should have been awarded the victory but the British boxer experienced the second defeat of his 28-bout professional journey.
The Champion Earns Victory in Dull Affair
His career development has plateaued in recent times through promotional disputes and considerable time of lack of fights.
Earlier forecast as the next star of the British fight scene, he now is positioned trying to realize his potential - possibly in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with both competitors ready to take risks in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after damaging his hand mid-fight, was participating in his second appearance at light heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who operated with a protective stance to narrowly win the cleaner periods.
The spectators' acceptance diminished because of frequent holding, with Parker falling to the floor multiple occasions during clinches.
Parker ended stronger, but many rounds were hard to judge. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
Buatsi progresses, but with the likes of power puncher David Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Hatton Homage Motivates All-Manchester Fight
In the co-main event, Lyndon Arthur overcame Rea by close verdict in a outstanding all-Manchester contest to win the European light-heavyweight championship.
The arena became quiet for a profoundly moving homage before the fight as ten bells sounded in remembrance of local hero Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised boxing event in the urban center since Hatton's passing. As the concluding sound ended, the silence transitioned to a chant of "there's just one Ricky Hatton".
The fighting during the bout matched the emotion. Arthur was floored by a significant blow flush on the face in the initial stage, standing uncertainly to his feet on the referee's count.
But the red-colored attire of the fighter soon pressed ahead again. From the other corner, Rea - in opposing blue - was injured quickly, noticeable damage forming under his orbital area as the fighters exchanged hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the pace rarely dropped over twelve rounds.
The victor barely secured the result with judges scorecards of 114-114, narrow lead and clearer margin, but each competitor were determined and courageous, everything their hero Hatton represented.
