British light heavyweight Buatsi earned a win yet disappointing beginning to his career under new promoters with a points victory over Zach Parker in Manchester.
The Olympic medal winner's work rate likely gained him a majority decision in a tight 10-round fight at the Manchester venue.
But the challenger found success, delivering effective clean blows in a fight where the techniques failed to mesh, with excessive holding disrupting the contest.
Two judges had it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best display but what defines champions? They succeed," Buatsi commented in the ring as he was faced boos from the spectators.
The British fighter bounced back after his initial pro loss - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Several boxing experts thought Parker, 31, merited the victory but the contender endured the second loss of his 28-fight professional journey.
The Champion Earns Triumph in Uneventful Encounter
The fighter's advancement has slowed in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the future of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with both competitors willing to take risks in a tentative opening few rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was participating in his second bout at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, making life awkward for the favorite, who operated with a protective stance to narrowly win the more effective rounds.
The audience's tolerance wore thin because of constant clinching, with the challenger slipping to the canvas various instances during close exchanges.
Parker closed well, but multiple periods were challenging to assess. However, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, giving Buatsi just a single round.
The victor progresses, but with the presence of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Memorial Inspires Local Rivalry Fight
In the co-main event, Lyndon Arthur beat Rea by split-decision in a terrific all-Manchester battle to win the European light heavyweight title.
The arena became quiet for a extremely emotional memorial before the fight as ten bells tolled in remembrance of Manchester's own Hatton, who succumbed at age 46 in last month.
It was the premier televised match card in the location since Hatton's passing. As the concluding sound ended, the quiet transitioned to a chant of "there's just one Ricky Hatton".
The action during the bout reflected the sentiment. Arthur was knocked down by a left hook squarely on the face in the second round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red equipment of the fighter soon advanced again. From the other corner, Rea - in rival City blue - was injured early, significant bruising appearing under his orbital area as the fighters exchanged powerful shots.
The challenger, 27, landed power punches but the champion, 34, responded in kind with effective uppercuts as the action rarely dropped over twelve rounds.
The victor barely secured the decision with official scores of 114-114, 115-113 and clearer margin, but both fighters were persistent and full of heart, all the qualities their hero Hatton stood for.
