UK light-heavyweight Buatsi made a winning yet unimpressive debut to his career under new promoters with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a close ten-round fight at the boxing arena.
But Parker had his moments, delivering effective individual punches in a fight where the techniques didn't complement each other, with constant grabbing marring the fight.
The scoring judges judged it 96-94 to Buatsi, with the final judge a 95-95.
"It wasn't my best performance but what defines champions? They win," Buatsi said in the arena as he was greeted with negative reactions from the crowd.
The Londoner bounced back after his first professional defeat - an epic battle with his previous opponent in last winter - to claim a twentieth professional win.
Some ringside observers thought Parker, thirty-one, deserved the win but the British boxer experienced the second loss of his 28-bout career.
The Champion Earns Victory in Slow Match
The fighter's advancement has stalled in the past few years through contract problems and long spells of lack of fights.
Previously predicted as the future of the British fight scene, he now finds himself trying to realize his potential - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with neither fighter willing to take risks in a tentative initial rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was competing in only his second fight at light heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for Buatsi, who worked behind a protective stance to narrowly win the more effective rounds.
The spectators' acceptance diminished amid constant clinching, with the challenger slipping to the canvas various instances during grappling.
Parker closed well, but several stanzas were challenging to assess. Nevertheless, previous titleholder Carl Frampton - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the likes of power puncher Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - based on this performance - still appears challenging.
Ricky Hatton Memorial Fuels Manchester Derby Contest
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a excellent local rivalry fight to secure the European light heavyweight title.
The venue became quiet for a profoundly moving memorial ahead of the contest as ten bells rang in remembrance of local hero Ricky Hatton, who died aged 46 in September.
It was the premier televised match card in the city since the passing of Hatton. As the final chime ended, the quiet gave way to a roar of "only one Ricky Hatton".
The fighting inside the ropes matched the feeling. Arthur was sent to the canvas by a left hook squarely on the face in the initial stage, rising shakily to his position on the count of eight.
But the red-colored shorts of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was injured early, significant bruising forming under his eye as the duo landed hard punches.
The challenger, 27, connected with strong blows but Arthur, 34, responded in kind with powerful upward punches as the intensity rarely dropped over the full distance.
The victor edged the decision with judges scorecards of even score, narrow lead and 115-112, but both fighters were determined and full of heart, exactly what their idol the legend stood for.
