British light heavyweight Buatsi earned a win yet disappointing debut to his career under new promoters with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a close 10-round fight at the Manchester venue.
But Parker landed significant shots, delivering effective individual punches in a match where the techniques didn't complement each other, with frequent clinching disrupting the action.
The scoring judges scored it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They win," the victor stated in the ringside as he was faced negative reactions from the spectators.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Various analysts believed Parker, thirty-one, deserved the victory but the Derbyshire fighter suffered the second loss of his 28-match career.
The Champion Claims Victory in Slow Match
His career development has stalled in the past few years through promotional disputes and considerable time of inactivity.
Earlier forecast as the future of the British fight scene, he now stands trying to achieve expectations - maybe in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers prepared to take risks in a calculated initial rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had made it competitive, making life awkward for the favorite, who worked behind a tight guard to narrowly win the better rounds.
The spectators' acceptance decreased amid constant clinching, with the challenger going down multiple occasions during grappling.
The underdog ended stronger, but many rounds were hard to judge. Although, ex-champion Carl Frampton - commentating on Dazn - had it particularly wide for Parker, scoring for Buatsi just a single round.
Buatsi moves on, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Homage Inspires All-Manchester Contest
In the co-main event, Arthur overcame Bradley Rea by split-decision in a outstanding all-Manchester fight to win the European light heavyweight belt.
The arena fell silent for a extremely emotional homage before the fight as a bell ceremony rang in remembrance of Manchester's own Hatton, who died at age 46 in last month.
It was the first major televised boxing event in the location since Hatton's death. As the last bell disappeared, the stillness transitioned to a chant of "there's just one Hatton".
The competition during the bout reflected the emotion. The eventual winner was knocked down by a left hook squarely on the chin in the initial stage, standing uncertainly to his position on the referee's count.
But the Manchester United-red shorts of Arthur soon came forward again. On the opposite side, the opponent - in opposing blue - was marked up quickly, significant bruising appearing under his face as the duo traded hard punches.
Rea, 27, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the action hardly diminished over 12 rounds.
Arthur narrowly won the decision with judges scorecards of even score, narrow lead and 115-112, but each competitor were persistent and full of heart, exactly what their inspiration the legend represented.
