British light-heavyweight Buatsi earned a win yet disappointing start to his career under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a split decision in a tight 10-round fight at the boxing arena.
But the challenger had his moments, delivering effective individual punches in a match where the styles never quite clicked, with excessive holding disrupting the fight.
The scoring judges had it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my finest display but how do champions respond? They succeed," Buatsi stated in the arena as he was faced disapproval from the spectators.
The Londoner bounced back after his initial pro loss - an epic battle with Callum Smith in last winter - to secure a 20th pro success.
Various analysts felt the challenger, thirty-one, merited the decision but the British boxer suffered the second setback of his 28-match professional journey.
The Champion Earns Victory in Uneventful Affair
Buatsi's progress has plateaued in the past few years through management issues and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now is positioned trying to realize his potential - perhaps in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with neither fighter prepared to be aggressive in a cagey opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after suffering a hand injury in the contest, was making just his second appearance at light-heavyweight.
By the middle rounds, Parker had stayed in contention, creating difficulties for the favorite, who operated with a protective stance to barely take the better rounds.
The crowd's patience diminished amid regular grabbing, with the challenger going down various instances during clinches.
Parker ended stronger, but several stanzas were hard to judge. Although, former world champion Carl Frampton - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the likes of hard hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Homage Fuels Manchester Derby Contest
In the co-main event, Lyndon Arthur defeated Rea by divided decision in a terrific all-Manchester fight to win the continental belt.
The venue became quiet for a extremely emotional memorial before the fight as ten bells sounded in honor of local hero Ricky Hatton, who succumbed aged 46 in last month.
It was the premier televised match card in the location since the passing of Hatton. As the final chime disappeared, the silence became a roar of "there's only one Hatton".
The action during the bout reflected the feeling. Arthur was sent to the canvas by a left hook squarely on the jaw in the early round, rising shakily to his position on the eight count.
But the traditional red attire of the fighter soon pressed ahead again. From the other corner, the opponent - in opposing blue - was injured quickly, heavy swelling forming under his eye as the duo landed punishing blows.
The challenger, 27, landed power punches but Arthur, 34, matched the intensity with effective uppercuts as the pace rarely dropped over 12 rounds.
Arthur edged the result with scoring tallies of 114-114, narrow lead and clearer margin, but the two athletes were determined and full of heart, all the qualities their idol the legend stood for.
