UK light heavyweight Buatsi secured a victory yet unimpressive beginning to life under recent management with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a majority decision in a close 10-round fight at the boxing arena.
But the challenger found success, delivering effective individual punches in a fight where the styles failed to mesh, with excessive holding spoiling the contest.
The scoring judges scored it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best display but how do champions respond? They win," Buatsi said in the arena as he was met by boos from the spectators.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers thought the challenger, 31, deserved the win but the British boxer endured the second defeat of his 28-match professional journey.
The Champion Secures Win in Uneventful Encounter
His career development has plateaued in recent years through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now is positioned trying to realize his potential - maybe in what seems like a final roll of the dice - under recent support.
He began cautiously, with neither fighter willing to overcommit in a cagey opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was making just his second bout at light heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for Buatsi, who worked behind a solid defense to barely take the cleaner rounds.
The spectators' acceptance diminished amid constant clinching, with the challenger going down several times during grappling.
Parker ended stronger, but multiple periods were hard to judge. However, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Tribute Inspires All-Manchester Fight
In the secondary fight, Arthur overcame Rea by divided decision in a outstanding all-Manchester battle to win the continental belt.
The stadium fell silent for a deeply poignant tribute before the fight as a bell ceremony rang in memory of the city's native Hatton, who died at age 46 in last month.
It was the initial significant broadcast match card in the location since Hatton's death. As the last bell ended, the silence transitioned to a chant of "there's only one Hatton".
The fighting inside the ropes matched the emotion. The eventual winner was knocked down by a powerful punch directly to the chin in the second round, getting up unsteadily to his position on the count of eight.
But the Manchester United-red equipment of the fighter soon came forward again. From the other corner, Rea - in competitive blue - was injured quickly, significant bruising appearing under his eye as the pair traded powerful shots.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with effective uppercuts as the pace rarely dropped over 12 rounds.
Arthur narrowly won the decision with judges scorecards of draw, close margin and wider gap, but the two athletes were determined and brave, exactly what their inspiration Hatton embodied.
