UK light-heavyweight Buatsi earned a win yet unimpressive start to life under new promoters with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a split decision in a close 10-round contest at the Co-op Live Arena.
But Parker had his moments, connecting with powerful individual punches in a contest where the styles never quite clicked, with frequent clinching spoiling the contest.
Two judges had it 96-94 to Buatsi, with the third a even score.
"It wasn't my finest showing but how do champions respond? They win," Buatsi said in the ringside as he was faced disapproval from the spectators.
The Londoner got back to winning after his first professional defeat - an thrilling contest with Callum Smith in last winter - to earn a twentieth professional win.
Several boxing experts felt the challenger, 31, should have been awarded the victory but the Derbyshire fighter endured the second loss of his 28-fight professional journey.
The Champion Claims Victory in Dull Encounter
His career development has stalled in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to achieve expectations - maybe in what appears to be a last chance - under fresh management.
He opened tentatively, with the two boxers ready to take risks in a tentative initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand during the bout, was participating in his second appearance at light heavyweight.
By the halfway stage, Parker had kept it close, causing problems for the favorite, who utilized a protective stance to barely take the better rounds.
The audience's tolerance decreased because of regular grabbing, with Parker falling to the floor multiple occasions during grappling.
The underdog closed well, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - working with Dazn - had it particularly wide for Parker, giving Buatsi just one round.
The victor advances, but with the presence of hard hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - judging by this showing - still seems difficult.
Hatton Tribute Motivates Manchester Derby Battle
In the secondary fight, Arthur beat Rea by split-decision in a terrific Manchester vs Manchester contest to capture the European light heavyweight title.
The venue became quiet for a profoundly moving homage ahead of the contest as 10 bells tolled in remembrance of local hero Ricky Hatton, who died at age 46 in September.
It was the premier televised match card in the location since Hatton's passing. As the final chime ended, the quiet gave way to a chant of "only one Hatton".
The fighting inside the ropes equaled the emotion. Arthur was knocked down by a powerful punch squarely on the jaw in the second round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red equipment of Arthur soon advanced again. Across the ring, Rea - in rival City blue - was damaged early, significant bruising developing under his orbital area as the pair exchanged hard punches.
Rea, 27, connected with strong blows but the champion, 34, responded in kind with powerful upward punches as the pace seldom decreased over twelve rounds.
The victor barely secured the verdict with scoring tallies of 114-114, 115-113 and 115-112, but the two athletes were relentless and full of heart, everything their hero the legend embodied.
