UK light heavyweight Buatsi made a winning yet disappointing start to his career under fresh promotional backing with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a judges' verdict in a close ten-round fight at the Co-op Live Arena.
But the challenger had his moments, landing some telling individual punches in a fight where the techniques didn't complement each other, with excessive holding spoiling the fight.
Two judges had it 96-94 to the winner, with the remaining official a even score.
"It wasn't my finest showing but what defines champions? They win," the victor stated in the ringside as he was greeted with boos from the spectators.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to claim a 20th pro success.
Some ringside observers believed Parker, thirty-one, should have been awarded the decision but the British boxer suffered the second defeat of his 28-bout career.
The Champion Earns Triumph in Dull Affair
His career development has stalled in recent times through contract problems and considerable time of inactivity.
Previously predicted as the rising talent of British boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with the two boxers willing to overcommit in a cagey early stages.
Parker, whose sole prior loss came at the lower weight class against John Ryder in 2022 after suffering a hand injury in the contest, was making just his second appearance at light-heavyweight.
By the middle rounds, Parker had stayed in contention, making life awkward for Buatsi, who worked behind a tight guard to narrowly win the more effective rounds.
The audience's tolerance wore thin during frequent holding, with Parker falling to the floor several times during close exchanges.
The underdog ended stronger, but several stanzas were challenging to assess. Although, previous titleholder Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi progresses, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Homage Inspires Manchester Derby Contest
In the co-main event, Lyndon Arthur overcame Bradley Rea by divided decision in a terrific all-Manchester fight to secure the European light-heavyweight belt.
The venue became quiet for a profoundly moving tribute ahead of the contest as 10 bells sounded in honor of Manchester's own Ricky Hatton, who died at age 46 in recently.
It was the first major televised fight night in the urban center since Hatton's death. As the concluding sound faded, the stillness transitioned to a chant of "there's just one Hatton".
The action during the bout reflected the feeling. The eventual winner was sent to the canvas by a powerful punch directly to the face in the second round, standing uncertainly to his feet on the eight count.
But the traditional red shorts of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was injured soon, significant bruising forming under his eye as the duo exchanged hard punches.
The challenger, 27, connected with strong blows but the champion, 34, fought fire with fire with effective uppercuts as the pace rarely dropped over the full distance.
Arthur edged the verdict with official scores of even score, narrow lead and wider gap, but the two athletes were persistent and full of heart, everything their inspiration the legend stood for.
