British light heavyweight Buatsi earned a win yet underwhelming beginning to his career under fresh promotional backing with a decision win over Zach Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a split decision in a tight 10-round contest at the Co-op Live Arena.
But the challenger had his moments, delivering effective individual punches in a contest where the approaches never quite clicked, with excessive holding spoiling the fight.
The scoring judges judged it 96-94 to Buatsi, with the final judge a 95-95.
"It wasn't my greatest display but how do champions respond? They succeed," the victor said in the arena as he was faced disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an thrilling contest with Callum Smith in last winter - to earn a 20th career victory.
Some ringside observers felt the challenger, thirty-one, merited the win but the British boxer endured the second loss of his 28-match career.
Buatsi Claims Triumph in Uneventful Encounter
Buatsi's progress has slowed in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the rising talent of British boxing, he now finds himself trying to achieve expectations - perhaps in what seems like a final roll of the dice - under fresh management.
He started carefully, with both competitors willing to take risks in a calculated early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after damaging his hand in the contest, was making just his second appearance at light heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for the favorite, who worked behind a solid defense to barely take the better stanzas.
The crowd's patience diminished because of constant clinching, with the challenger falling to the floor several times during grappling.
Parker finished the stronger, but several stanzas were challenging to assess. However, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, giving Buatsi just only one stanza.
The victor progresses, but with the presence of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Homage Fuels Manchester Derby Battle
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a terrific Manchester vs Manchester fight to win the continental title.
The venue fell silent for a profoundly moving homage before the fight as a bell ceremony rang in memory of Manchester's own Ricky Hatton, who passed away at age 46 in last month.
It was the initial significant broadcast match card in the city since Hatton's death. As the final chime faded, the quiet transitioned to a roar of "only one Ricky Hatton".
The fighting inside the ropes reflected the sentiment. The eventual winner was floored by a left hook directly to the jaw in the initial stage, getting up unsteadily to his footing on the referee's count.
But the traditional red attire of the fighter soon pressed ahead again. Across the ring, Rea - in competitive blue - was injured soon, significant bruising developing under his orbital area as the pair exchanged powerful shots.
The challenger, twenty-seven, landed power punches but the champion, 34, responded in kind with powerful upward punches as the intensity seldom decreased over the full distance.
Arthur edged the result with judges scorecards of 114-114, close margin and wider gap, but the two athletes were determined and brave, everything their hero Hatton stood for.
