UK light heavyweight Buatsi secured a victory yet disappointing start to his career under new promoters with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a majority decision in a competitive ten-round bout at the Co-op Live Arena.
But the challenger found success, delivering effective single shots in a match where the techniques failed to mesh, with frequent clinching spoiling the contest.
The scoring judges had it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my finest display but what defines champions? They succeed," Buatsi said in the ring as he was faced disapproval from the crowd.
The Londoner bounced back after his first professional defeat - an thrilling contest with Callum Smith in February - to secure a twentieth professional win.
Some ringside observers felt Parker, 31, should have been awarded the victory but the Derbyshire fighter suffered the second defeat of his 28-fight career.
The Champion Secures Win in Slow Encounter
Buatsi's progress has plateaued in recent times through contract problems and considerable time of inactivity.
Once tipped as the future of British boxing, he now stands trying to achieve expectations - maybe in what seems like a last chance - under recent support.
He started carefully, with neither fighter ready to take risks in a tentative opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was participating in his second bout at light-heavyweight.
By the halfway stage, Parker had stayed in contention, making life awkward for the favorite, who worked behind a solid defense to edge the more effective periods.
The audience's tolerance wore thin because of regular grabbing, with Parker slipping to the canvas multiple occasions during close exchanges.
The underdog closed well, but several stanzas were hard to judge. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor progresses, but with the likes of power puncher Benavidez, and Russian star Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Memorial Fuels Manchester Derby Contest
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a terrific local rivalry fight to capture the European light-heavyweight championship.
The arena fell silent for a deeply poignant tribute ahead of the contest as ten bells tolled in remembrance of local hero Ricky Hatton, who passed away at age 46 in September.
It was the initial significant broadcast fight night in the location since Hatton's death. As the last bell disappeared, the stillness became a roar of "there's only one Ricky Hatton".
The competition inside the ropes reflected the emotion. Arthur was sent to the canvas by a significant blow directly to the jaw in the second round, standing uncertainly to his footing on the eight count.
But the traditional red shorts of the fighter soon came forward again. On the opposite side, Rea - in competitive blue - was injured quickly, significant bruising forming under his eye as the duo exchanged powerful shots.
The challenger, 27, delivered effective strikes but the champion, 34, fought fire with fire with stinging uppercuts as the pace rarely dropped over twelve rounds.
Arthur edged the verdict with judges scorecards of 114-114, 115-113 and wider gap, but both fighters were persistent and full of heart, exactly what their inspiration the legend stood for.
