British light heavyweight Buatsi secured a victory yet unimpressive beginning to his career under new promoters with a points victory over Zach Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a majority decision in a tight 10-round contest at the boxing arena.
But Parker had his moments, landing some telling individual punches in a match where the approaches didn't complement each other, with constant grabbing spoiling the contest.
Two judges scored it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my finest display but what do champions do? They win," Buatsi said in the ring as he was greeted with disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts believed Parker, thirty-one, should have been awarded the victory but the British boxer experienced the second setback of his 28-match professional journey.
The Champion Earns Triumph in Dull Affair
Buatsi's progress has plateaued in recent times through contract problems and extended periods of lack of fights.
Once tipped as the rising talent of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors prepared to be aggressive in a calculated early stages.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand mid-fight, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who operated with a protective stance to edge the cleaner rounds.
The spectators' acceptance decreased amid constant clinching, with the challenger going down various instances during clinches.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, ex-champion Carl Frampton - providing analysis for Dazn - 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 ruling the division, the journey to titles - on this evidence - still appears challenging.
Hatton Homage Inspires Local Rivalry Contest
In the supporting bout, Lyndon Arthur overcame Rea by split-decision in a terrific Manchester vs Manchester fight to capture the continental title.
The arena became quiet for a profoundly moving tribute before the fight as 10 bells sounded in honor of local hero Ricky Hatton, who died 46 years old in September.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the final chime faded, the silence gave way to a shout of "there's only one Ricky Hatton".
The action inside the ropes reflected the emotion. Arthur was sent to the canvas by a significant blow flush on the chin in the early round, standing uncertainly to his position on the referee's count.
But the Manchester United-red equipment of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was injured quickly, noticeable damage appearing under his face as the pair traded hard punches.
Rea, 27, landed power punches but the champion, thirty-four, responded in kind with powerful upward punches as the intensity seldom decreased over twelve rounds.
Arthur barely secured the decision with judges scorecards of draw, narrow lead and wider gap, but both fighters were relentless and brave, all the qualities their idol the legend embodied.
