British light-heavyweight Buatsi made a winning yet underwhelming start to life under new promoters with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a majority decision in a tight ten-round fight at the boxing arena.
But Parker found success, connecting with powerful individual punches in a match where the techniques never quite clicked, with excessive holding disrupting the fight.
The scoring judges had it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my best display but what defines champions? They win," Buatsi commented in the ring as he was faced boos from the crowd.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in February - to claim a 20th pro success.
Various analysts believed Parker, 31, should have been awarded the decision but the British boxer suffered the second loss of his 28-fight career.
The Champion Earns Victory in Uneventful Encounter
His career development has plateaued in recent times through management issues and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what feels like a last chance - under new promotional backing.
He opened tentatively, with both competitors ready to be aggressive in a tentative early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who utilized a solid defense to barely take the better rounds.
The crowd's patience decreased during regular grabbing, with Parker going down several times during clinches.
Parker finished the stronger, but several stanzas were challenging to assess. Although, previous titleholder Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi advances, but with the caliber of heavy hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Memorial Motivates Local Rivalry Battle
In the co-main event, Arthur defeated Rea by close verdict in a terrific Manchester vs Manchester fight to secure the European light-heavyweight belt.
The venue became quiet for a profoundly moving tribute before the fight as 10 bells sounded in honor of the city's native Hatton, who passed away at age 46 in September.
It was the first major televised boxing event in the location since Hatton's passing. As the final chime faded, the stillness gave way to a roar of "there's only one Hatton".
The action within the ring equaled the feeling. The eventual winner was knocked down by a left hook flush on the face in the second round, standing uncertainly to his feet on the eight count.
But the traditional red attire of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was marked up early, noticeable damage developing under his face as the pair exchanged powerful shots.
Rea, 27, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity hardly diminished over twelve rounds.
Arthur narrowly won the verdict with official scores of even score, close margin and clearer margin, but both fighters were relentless and full of heart, everything their idol Hatton represented.
