UK light-heavyweight Buatsi earned a win yet disappointing debut to life under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a tight 10-round fight at the Co-op Live Arena.
But the challenger had his moments, landing some telling individual punches in a contest where the techniques never quite clicked, with frequent clinching marring the contest.
The officials judged it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my greatest performance but what do champions do? They succeed," Buatsi said in the ring as he was faced disapproval from the audience.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to claim a 20th pro success.
Some ringside observers felt Parker, 31, deserved the victory but the contender experienced the second setback of his 28-fight professional journey.
Buatsi Claims Triumph in Slow Match
Buatsi's progress has stalled in the past few years through promotional disputes and extended periods of lack of fights.
Once tipped as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors ready to take risks in a tentative initial rounds.
Parker, whose only previous defeat came at super middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was participating in his second bout at light-heavyweight.
By the fight's midpoint, Parker had kept it close, causing problems for the favorite, who operated with a protective stance to barely take the cleaner periods.
The crowd's patience wore thin amid frequent holding, with Parker slipping to the canvas multiple occasions during grappling.
Parker closed well, but several stanzas were difficult to score. Although, former world champion the boxing analyst - working with the broadcast network - had it particularly wide for Parker, awarding Buatsi just one round.
The victor advances, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Homage Motivates Local Rivalry Fight
In the secondary fight, Lyndon Arthur overcame Rea by close verdict in a outstanding local rivalry battle to secure the European light heavyweight title.
The arena grew hushed for a deeply poignant memorial ahead of the contest as a bell ceremony sounded in memory of Manchester's own Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the final chime disappeared, the quiet became a shout of "there's just one Hatton".
The fighting during the bout reflected the emotion. Arthur was floored by a left hook directly to the chin in the second round, rising shakily to his feet on the count of eight.
But the Manchester United-red equipment of Arthur soon pressed ahead again. From the other corner, Rea - in rival City blue - was damaged early, noticeable damage developing under his face as the pair exchanged hard punches.
The challenger, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace seldom decreased over 12 rounds.
Arthur edged the decision with judges scorecards of even score, close margin and 115-112, but each competitor were determined and courageous, everything their hero the legend stood for.
