British light heavyweight Buatsi secured a victory yet disappointing start to life under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a majority decision in a tight 10-round fight at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective individual punches in a fight where the styles never quite clicked, with constant grabbing disrupting the action.
Two judges had it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest performance but what do champions do? They prevail," Buatsi said in the ring as he was greeted with negative reactions from the crowd.
The British fighter bounced back after his initial pro loss - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Some ringside observers thought the challenger, 31, should have been awarded the decision but the British boxer endured the second setback of his 28-fight career.
Buatsi Secures Win in Dull Encounter
His career development has plateaued in recent times through management issues and considerable time of inactivity.
Previously predicted as the future of British boxing, he now finds himself trying to fulfil that early promise - possibly in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors prepared to be aggressive in a calculated initial rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was participating in his second bout at light heavyweight.
By the halfway stage, Parker had kept it close, causing problems for the favorite, who utilized a tight guard to edge the better periods.
The crowd's patience wore thin because of constant clinching, with the challenger slipping to the canvas several times during clinches.
The underdog ended stronger, but multiple periods were hard to judge. However, previous titleholder the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the caliber 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 Homage Fuels All-Manchester Fight
In the supporting bout, Arthur beat Rea by divided decision in a excellent all-Manchester fight to capture the continental championship.
The stadium became quiet for a profoundly moving tribute ahead of the contest as a bell ceremony tolled in memory of local hero Ricky Hatton, who passed away aged 46 in recently.
It was the first major televised boxing event in the urban center since Hatton's passing. As the final chime faded, the quiet transitioned to a roar of "there's only one Hatton".
The competition within the ring equaled the emotion. Arthur was sent to the canvas by a significant blow directly to the chin in the second round, rising shakily to his feet on the count of eight.
But the red-colored equipment of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was injured early, noticeable damage forming under his eye as the pair landed powerful shots.
Rea, 27, landed power punches but Arthur, thirty-four, matched the intensity with powerful upward punches as the intensity rarely dropped over the full distance.
The victor barely secured the decision with judges scorecards of 114-114, close margin and wider gap, but both fighters were persistent and brave, exactly what their hero Hatton stood for.
