British light heavyweight Buatsi earned a win yet disappointing beginning to his career under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a close ten-round bout at the Manchester venue.
But Parker landed significant shots, connecting with powerful clean blows in a fight where the styles never quite clicked, with frequent clinching marring the contest.
Two judges judged it 96-94 to the winner, with the remaining official a even score.
"It wasn't my best performance but what defines champions? They prevail," Buatsi said in the arena as he was met by disapproval from the spectators.
The British fighter bounced back after his initial pro loss - an memorable fight with Callum Smith in February - to secure a 20th pro success.
Several boxing experts felt Parker, 31, should have been awarded the victory but the Derbyshire fighter suffered the second defeat of his 28-bout career.
Buatsi Earns Victory in Slow Affair
Buatsi's progress has slowed in recent years through contract problems and long spells of inactivity.
Previously predicted as the rising talent of UK boxing, he now finds himself trying to realize his potential - maybe in what feels like a ultimate opportunity - under recent support.
He started carefully, with both competitors willing to be aggressive in a cagey early stages.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in two years ago after damaging his hand during the bout, was participating in his second bout at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for Buatsi, who utilized a protective stance to narrowly win the more effective periods.
The audience's tolerance decreased amid constant clinching, with Parker slipping to the canvas multiple occasions during clinches.
Parker ended stronger, but many rounds were hard to judge. Although, ex-champion Carl Frampton - commentating on Dazn - had it strongly leaning for Parker, giving Buatsi just only one stanza.
The victor advances, but with the presence of hard hitter Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Memorial Motivates Manchester Derby Battle
In the co-main event, Arthur beat Rea by split-decision in a excellent local rivalry fight to win the European light heavyweight title.
The venue became quiet for a deeply poignant memorial prior to the bout as ten bells tolled in honor of the city's native Hatton, who passed away 46 years old in last month.
It was the first major televised fight night in the city since the passing of Hatton. As the last bell disappeared, the quiet became a shout of "there's only one Ricky Hatton".
The fighting within the ring equaled the sentiment. The eventual winner was floored by a powerful punch directly to the face in the early round, getting up unsteadily to his footing on the referee's count.
But the traditional red shorts of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was damaged soon, significant bruising forming under his face as the fighters traded hard punches.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with effective uppercuts as the intensity seldom decreased over the full distance.
Arthur narrowly won the verdict with official scores of draw, close margin and clearer margin, but each competitor were determined and courageous, all the qualities their inspiration the legend represented.
