British light heavyweight Buatsi secured a victory yet disappointing debut to his career under fresh promotional backing with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a tight 10-round contest at the Co-op Live Arena.
But Parker found success, connecting with powerful single shots in a contest where the styles didn't complement each other, with frequent clinching marring the contest.
The scoring judges judged it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest display but how do champions respond? They prevail," the victor commented in the arena as he was met by disapproval from the crowd.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in February - to claim a 20th career victory.
Various analysts believed the challenger, 31, deserved the win but the Derbyshire fighter suffered the second setback of his 28-bout career.
The Champion Earns Triumph in Slow Match
His career development has stalled in recent years through contract problems and considerable time of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to achieve expectations - possibly in what seems like a final roll of the dice - under fresh management.
He began cautiously, with the two boxers ready to take risks in a tentative initial rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in 2022 after suffering a hand injury in the contest, was competing in only his second bout at the higher weight class.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who worked behind a protective stance to edge the more effective rounds.
The spectators' acceptance decreased amid constant clinching, with Parker slipping to the canvas various instances during clinches.
Parker finished the stronger, but multiple periods were challenging to assess. Nevertheless, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the presence of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Fuels Manchester Derby Battle
In the co-main event, Arthur beat Rea by close verdict in a outstanding Manchester vs Manchester contest to win the continental championship.
The stadium became quiet for a profoundly moving tribute before the fight as 10 bells sounded in honor of local hero Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the concluding sound faded, the stillness gave way to a shout of "there's just one Hatton".
The competition within the ring matched the sentiment. The eventual winner was sent to the canvas by a significant blow flush on the chin in the initial stage, standing uncertainly to his position on the referee's count.
But the red-colored attire of Arthur soon came forward again. From the other corner, the opponent - in rival City blue - was injured quickly, significant bruising appearing under his orbital area as the pair exchanged powerful shots.
Rea, 27, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the intensity hardly diminished over the full distance.
Arthur barely secured the verdict with scoring tallies of even score, narrow lead and wider gap, but each competitor were relentless and brave, all the qualities their idol Hatton stood for.
