UK light heavyweight Buatsi made a winning yet disappointing start to life under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a judges' verdict in a tight ten-round bout at the Manchester venue.
But the challenger had his moments, delivering effective individual punches in a contest where the approaches failed to mesh, with excessive holding disrupting the fight.
Two judges judged it 96-94 in favor to the winner, with the third a even score.
"It wasn't my greatest performance but what defines champions? They win," Buatsi said in the ringside as he was faced boos from the crowd.
The Londoner bounced back after his maiden career setback - an memorable fight with Callum Smith in February - to claim a 20th career victory.
Several boxing experts thought the challenger, 31, merited the victory but the contender experienced the second setback of his 28-match professional journey.
Buatsi Claims Win in Dull Affair
The fighter's advancement has stalled in recent times through promotional disputes and long spells of lack of fights.
Earlier forecast as the future of the British fight scene, he now stands trying to achieve expectations - possibly in what seems like a last chance - under new promotional backing.
He started carefully, with both competitors prepared to overcommit in a tentative initial rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was participating in his second fight at light heavyweight.
By the middle rounds, the underdog had kept it close, causing problems for Buatsi, who worked behind a protective stance to edge the more effective rounds.
The audience's tolerance decreased because of regular grabbing, with Parker slipping to the canvas various instances during grappling.
Parker finished the stronger, but many rounds were difficult to score. Nevertheless, former world champion the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
The victor advances, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Fuels All-Manchester Fight
In the co-main event, Lyndon Arthur overcame Rea by split-decision in a terrific Manchester vs Manchester fight to win the European light heavyweight belt.
The stadium grew hushed for a deeply poignant memorial prior to the bout as ten bells rang in remembrance of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the concluding sound faded, the quiet gave way to a roar of "there's just one Ricky Hatton".
The action inside the ropes equaled the feeling. Arthur was knocked down by a left hook flush on the jaw in the second round, standing uncertainly to his position on the referee's count.
But the Manchester United-red attire of the fighter soon came forward again. From the other corner, Rea - in competitive blue - was marked up soon, heavy swelling forming under his eye as the fighters landed powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over the full distance.
Arthur barely secured the decision with scoring tallies of draw, 115-113 and 115-112, but the two athletes were relentless and courageous, all the qualities their inspiration the legend embodied.
