UK light-heavyweight Buatsi earned a win yet unimpressive debut to his career under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a tight 10-round fight at the Co-op Live Arena.
But Parker had his moments, connecting with powerful single shots in a match where the techniques failed to mesh, with constant grabbing spoiling the contest.
Two judges had it 96-94 to Buatsi, with the final judge a 95-95.
"It wasn't my greatest showing but what do champions do? They win," the victor said in the ringside as he was greeted with disapproval from the audience.
The Londoner bounced back after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a twentieth professional win.
Several boxing experts felt the challenger, 31, deserved the win but the contender endured the second setback of his 28-fight career.
The Champion Earns Triumph in Dull Match
The fighter's advancement has stalled in the past few years through contract problems and long spells of inactivity.
Earlier forecast as the future of British boxing, he now stands trying to fulfil that early promise - maybe in what feels like a final roll of the dice - under recent support.
He began cautiously, with the two boxers willing to be aggressive in a calculated initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was making just his second appearance at light heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a tight guard to narrowly win the more effective stanzas.
The audience's tolerance diminished because of constant clinching, with Parker slipping to the canvas several times during grappling.
The underdog ended stronger, but multiple periods were hard to judge. Although, former world champion Carl Frampton - working with Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
Buatsi moves on, but with the likes of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Tribute Fuels Manchester Derby Contest
In the co-main event, Arthur defeated Rea by divided decision in a terrific Manchester vs Manchester battle to secure the European light heavyweight title.
The stadium fell silent for a profoundly moving homage ahead of the contest as a bell ceremony rang in honor of the city's native Hatton, who succumbed at age 46 in recently.
It was the first major televised match card in the location since Hatton's death. As the last bell ended, the stillness transitioned to a roar of "there's only one Ricky Hatton".
The fighting inside the ropes matched the sentiment. The eventual winner was sent to the canvas by a significant blow directly to the chin in the initial stage, getting up unsteadily to his feet on the referee's count.
But the traditional red attire of Arthur soon pressed ahead again. Across the ring, the opponent - in rival City blue - was injured soon, heavy swelling developing under his face as the pair landed hard punches.
Rea, twenty-seven, landed power punches but the champion, 34, responded in kind with effective uppercuts as the intensity seldom decreased over the full distance.
Arthur narrowly won the decision with official scores of 114-114, 115-113 and clearer margin, but each competitor were determined and full of heart, everything their idol Hatton stood for.
