UK light heavyweight Buatsi made a winning yet unimpressive beginning to his career under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a competitive ten-round fight at the Manchester venue.
But the challenger had his moments, delivering effective clean blows in a match where the styles failed to mesh, with frequent clinching disrupting the contest.
Two judges scored it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my finest performance but what do champions do? They prevail," the victor commented in the ringside as he was greeted with disapproval from the crowd.
The British fighter got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to claim a 20th pro success.
Several boxing experts believed the challenger, 31, merited the decision but the British boxer experienced the second setback of his 28-match professional journey.
The Champion Earns Win in Slow Affair
Buatsi's progress has stalled in recent times through promotional disputes and long spells of inactivity.
Once tipped as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - maybe in what appears to be a last chance - under new promotional backing.
He began cautiously, with neither fighter prepared to take risks in a tentative opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after breaking his hand during the bout, was participating in his second bout at light heavyweight.
By the middle rounds, the underdog had kept it close, causing problems for Buatsi, who operated with a solid defense to narrowly win the better periods.
The audience's tolerance diminished amid constant clinching, with the challenger slipping to the canvas various instances during close exchanges.
Parker closed well, but several stanzas were hard to judge. Although, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Hatton Memorial Motivates Manchester Derby Contest
In the secondary fight, Lyndon Arthur overcame Rea by split-decision in a excellent all-Manchester contest to secure the European light-heavyweight title.
The stadium became quiet for a profoundly moving homage before the fight as ten bells tolled in remembrance of the city's native Hatton, who died aged 46 in September.
It was the first major televised match card in the urban center since the passing of Hatton. As the concluding sound faded, the silence gave way to a chant of "there's only one Ricky Hatton".
The competition during the bout reflected the feeling. Arthur was floored by a significant blow squarely on the face in the second round, standing uncertainly to his footing on the count of eight.
But the traditional red shorts of Arthur soon pressed ahead again. From the other corner, the opponent - in opposing blue - was injured soon, significant bruising appearing under his face as the fighters traded hard punches.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with effective uppercuts as the action hardly diminished over 12 rounds.
The victor barely secured the verdict with judges scorecards of even score, close margin and clearer margin, but both fighters were relentless and brave, everything their idol Hatton stood for.
