British light-heavyweight Buatsi earned a win yet unimpressive start to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a competitive 10-round fight at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful clean blows in a match where the approaches didn't complement each other, with excessive holding spoiling the contest.
The officials scored it 96-94 for to the winner, with the third a even score.
"It wasn't my finest performance but what do champions do? They prevail," the victor said in the ringside as he was met by disapproval from the audience.
The Londoner got back to winning after his first professional defeat - an memorable fight with his previous opponent in February - to claim a twentieth professional win.
Various analysts believed the challenger, thirty-one, merited the victory but the Derbyshire fighter endured the second setback of his 28-fight professional journey.
Buatsi Secures Victory in Uneventful Affair
Buatsi's progress has plateaued in recent times through promotional disputes and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a last chance - under new promotional backing.
He started carefully, with the two boxers willing to be aggressive in a cagey opening few rounds.
Parker, whose only previous defeat came at super middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was making just his second appearance at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a solid defense to edge the more effective rounds.
The spectators' acceptance diminished amid frequent holding, with the challenger going down multiple occasions during close exchanges.
Parker closed well, but several stanzas were challenging to assess. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just one round.
The victor progresses, but with the likes of heavy hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still appears challenging.
Hatton Tribute Inspires All-Manchester Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding all-Manchester battle to secure the continental title.
The arena grew hushed for a profoundly moving homage prior to the bout as ten bells sounded in honor of Manchester's own Hatton, who passed away 46 years old in September.
It was the first major televised fight night in the city since Hatton's death. As the concluding sound ended, the silence became a chant of "there's only one Ricky Hatton".
The fighting during the bout reflected the sentiment. The eventual winner was floored by a powerful punch directly to the face in the early round, getting up unsteadily to his footing on the eight count.
But the red-colored shorts of the fighter soon advanced again. From the other corner, the opponent - in competitive blue - was injured quickly, significant bruising forming under his eye as the duo traded punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity hardly diminished over twelve rounds.
The victor edged the verdict with judges scorecards of even score, close margin and clearer margin, but the two athletes were persistent and full of heart, everything their hero Hatton embodied.
