UK light heavyweight Buatsi earned a win yet disappointing beginning to his career under fresh promotional backing with a decision win over Zach Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling single shots in a fight where the techniques didn't complement each other, with frequent clinching marring the contest.
The officials scored it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my best performance but what do champions do? They succeed," Buatsi commented in the ringside as he was faced disapproval from the audience.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Several boxing experts felt the challenger, thirty-one, deserved the decision but the Derbyshire fighter experienced the second setback of his 28-match career.
Buatsi Claims Victory in Uneventful Affair
His career development has slowed in recent years through management issues and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to fulfil that early promise - maybe in what feels like a last chance - under fresh management.
He started carefully, with the two boxers ready to take risks in a calculated initial rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after breaking his hand during the bout, was competing in only his second fight at light heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who operated with a protective stance to barely take the more effective stanzas.
The spectators' acceptance diminished during frequent holding, with Parker falling to the floor various instances during grappling.
The underdog finished the stronger, but many rounds were hard to judge. Nevertheless, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Inspires All-Manchester Battle
In the secondary fight, Lyndon Arthur beat Rea by close verdict in a excellent all-Manchester contest to secure the European light-heavyweight championship.
The stadium became quiet for a deeply poignant tribute before the fight as ten bells sounded in memory of local hero Ricky Hatton, who passed away 46 years old in recently.
It was the first major televised match card in the location since the passing of Hatton. As the final chime ended, the silence became a chant of "there's only one Ricky Hatton".
The action inside the ropes matched the feeling. Arthur was knocked down by a powerful punch squarely on the face in the early round, standing uncertainly to his position on the eight count.
But the Manchester United-red attire of Arthur soon pressed ahead again. From the other corner, Rea - in competitive blue - was injured quickly, noticeable damage forming under his face as the pair landed powerful shots.
The challenger, 27, delivered effective strikes but the champion, 34, fought fire with fire with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor barely secured the decision with official scores of even score, close margin and clearer margin, but both fighters were determined and brave, all the qualities their hero Hatton embodied.
