British light heavyweight Buatsi secured a victory yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's work rate likely gained him a split decision in a close 10-round fight at the Manchester venue.
But Parker had his moments, delivering effective clean blows in a contest where the techniques never quite clicked, with excessive holding disrupting the action.
Two judges had it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest performance but what defines champions? They prevail," Buatsi commented in the ringside as he was met by boos from the audience.
The Londoner bounced back after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Several boxing experts believed the challenger, thirty-one, deserved the decision but the contender endured the second setback of his 28-bout career.
Buatsi Claims Win in Slow Match
Buatsi's progress has stalled in recent years through contract problems and considerable time of inactivity.
Previously predicted as the future 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 began cautiously, with the two boxers prepared to overcommit in a tentative early stages.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand in the contest, was participating in his second bout at light heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for Buatsi, who operated with a protective stance to edge the cleaner rounds.
The crowd's patience decreased during frequent holding, with the challenger falling to the floor multiple occasions during grappling.
The underdog ended stronger, but multiple periods were hard to judge. However, ex-champion the boxing analyst - working with Dazn - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the likes of power puncher David Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Memorial Fuels All-Manchester Fight
In the secondary fight, Lyndon Arthur overcame Rea by divided decision in a excellent all-Manchester battle to capture the European light heavyweight championship.
The arena fell silent for a profoundly moving tribute prior to the bout as 10 bells sounded in memory of Manchester's own Ricky Hatton, who passed away aged 46 in recently.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the concluding sound disappeared, the stillness transitioned to a chant of "only one Hatton".
The fighting within the ring matched the emotion. Arthur was sent to the canvas by a significant blow flush on the jaw in the second round, standing uncertainly to his footing on the eight count.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in rival City blue - was injured soon, heavy swelling developing under his orbital area as the fighters exchanged hard punches.
Rea, 27, delivered effective strikes but the champion, 34, responded in kind with powerful upward punches as the pace seldom decreased over 12 rounds.
Arthur edged the decision with official scores of 114-114, narrow lead and clearer margin, but both fighters were relentless and brave, everything their hero Hatton embodied.
