UK light heavyweight Buatsi secured a victory yet disappointing debut to his career under new promoters with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a competitive 10-round fight at the Co-op Live Arena.
But Parker landed significant shots, landing some telling clean blows in a fight where the techniques never quite clicked, with frequent clinching spoiling the fight.
Two judges scored it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my best showing but how do champions respond? They win," the victor stated in the ring as he was faced disapproval from the spectators.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to earn a twentieth professional win.
Various analysts felt the challenger, thirty-one, merited the win but the contender endured the second defeat of his 28-bout career.
The Champion Earns Triumph in Uneventful Match
Buatsi's progress has stalled in the past few years through management issues and considerable time of lack of fights.
Once tipped as the future of British boxing, he now stands trying to realize his potential - possibly in what feels like a final roll of the dice - under fresh management.
He began cautiously, with neither fighter ready to overcommit in a tentative initial rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in two years ago after damaging his hand in the contest, was making just his second fight at light heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for the favorite, who operated with a solid defense to barely take the better periods.
The crowd's patience decreased because of constant clinching, with the challenger going down various instances during clinches.
Parker closed well, but many rounds were hard to judge. Nevertheless, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for Parker, awarding Buatsi just one round.
The victor progresses, but with the likes of hard hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Memorial Motivates All-Manchester Contest
In the secondary fight, Lyndon Arthur defeated Rea by close verdict in a terrific all-Manchester battle to win the European light heavyweight championship.
The arena grew hushed for a extremely emotional homage ahead of the contest as 10 bells sounded in honor of the city's native Ricky Hatton, who died aged 46 in September.
It was the first major televised fight night in the city since Hatton's passing. As the concluding sound ended, the silence gave way to a chant of "there's only one Hatton".
The competition inside the ropes equaled the feeling. Arthur was floored by a significant blow flush on the chin in the initial stage, rising shakily to his footing on the eight count.
But the traditional red attire of the fighter soon came forward again. From the other corner, Rea - in competitive blue - was damaged early, heavy swelling appearing under his eye as the duo exchanged hard punches.
The challenger, 27, delivered effective strikes but Arthur, 34, matched the intensity with powerful upward punches as the pace hardly diminished over 12 rounds.
The victor narrowly won the decision with official scores of draw, 115-113 and clearer margin, but both fighters were determined and courageous, all the qualities their idol the legend embodied.
