UK light heavyweight Buatsi made a winning yet underwhelming beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a majority decision in a tight ten-round fight at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling individual punches in a contest where the styles never quite clicked, with frequent clinching marring the action.
Two judges scored it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my finest performance but how do champions respond? They win," Buatsi commented in the arena as he was met by boos from the audience.
The Londoner bounced back after his first professional defeat - an epic battle with Callum Smith in last winter - to earn a 20th career victory.
Some ringside observers thought Parker, thirty-one, deserved the decision but the contender suffered the second defeat of his 28-fight professional journey.
Buatsi Secures Win in Uneventful Match
Buatsi's progress has plateaued in the past few years through contract problems and long spells of lack of fights.
Previously predicted as the future of UK boxing, he now finds himself trying to realize his potential - maybe in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with both competitors ready to be aggressive in a tentative initial rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in 2022 after breaking his hand in the contest, was making just his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a solid defense to barely take the cleaner periods.
The audience's tolerance decreased amid frequent holding, with the challenger falling to the floor several times during clinches.
Parker closed well, but multiple periods were difficult to score. However, ex-champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
The victor advances, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Memorial Motivates All-Manchester Fight
In the co-main event, Arthur overcame Bradley Rea by divided decision in a terrific all-Manchester contest to win the European light heavyweight belt.
The stadium became quiet for a deeply poignant memorial ahead of the contest as a bell ceremony rang in honor of local hero Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the last bell ended, the stillness gave way to a chant of "there's just one Hatton".
The fighting within the ring matched the feeling. The eventual winner was knocked down by a left hook squarely on the jaw in the second round, getting up unsteadily to his footing on the eight count.
But the red-colored shorts of the fighter soon advanced again. On the opposite side, Rea - in rival City blue - was injured soon, significant bruising appearing under his face as the pair traded powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with powerful upward punches as the action rarely dropped over the full distance.
Arthur narrowly won the result with official scores of 114-114, 115-113 and 115-112, but each competitor were determined and courageous, exactly what their idol Hatton represented.
