British light heavyweight Buatsi earned a win yet disappointing beginning to his career under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a tight 10-round contest at the boxing arena.
But Parker found success, delivering effective individual punches in a match where the approaches never quite clicked, with constant grabbing spoiling the action.
The scoring judges scored it 96-94 for to the winner, with the final judge a 95-95.
"It wasn't my finest performance but what defines champions? They prevail," Buatsi said in the ringside as he was greeted with disapproval from the audience.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Some ringside observers believed Parker, 31, should have been awarded the win but the British boxer endured the second defeat of his 28-bout professional journey.
Buatsi Secures Win in Dull Affair
Buatsi's progress has stalled in the past few years through promotional disputes and long spells of inactivity.
Earlier forecast as the future of British boxing, he now is positioned trying to achieve expectations - possibly in what seems like a last chance - under fresh management.
He began cautiously, with the two boxers willing to be aggressive in a cagey early stages.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after breaking his hand during the bout, was making just his second appearance at light heavyweight.
By the middle rounds, Parker had kept it close, causing problems for Buatsi, who worked behind a tight guard to barely take the cleaner rounds.
The spectators' acceptance wore thin amid constant clinching, with Parker falling to the floor various instances during close exchanges.
The underdog ended stronger, but multiple periods were difficult to score. Although, former world champion Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the likes of power puncher David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Hatton Homage Motivates Local Rivalry Fight
In the secondary fight, Arthur beat Rea by close verdict in a excellent all-Manchester contest to capture the European light-heavyweight championship.
The stadium grew hushed for a profoundly moving memorial before the fight as a bell ceremony sounded in honor of local hero Ricky Hatton, who passed away aged 46 in recently.
It was the premier televised match card in the urban center since Hatton's passing. As the concluding sound disappeared, the stillness gave way to a chant of "there's just one Hatton".
The competition within the ring reflected the emotion. The eventual winner was knocked down by a powerful punch flush on the jaw in the initial stage, standing uncertainly to his footing on the eight count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was injured quickly, significant bruising forming under his face as the pair landed punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the intensity seldom decreased over 12 rounds.
Arthur barely secured the verdict with judges scorecards of 114-114, close margin and clearer margin, but both fighters were persistent and brave, all the qualities their idol Hatton embodied.
