British light-heavyweight Buatsi earned a win yet unimpressive debut to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a competitive 10-round fight at the Manchester venue.
But Parker landed significant shots, connecting with powerful clean blows in a match where the styles failed to mesh, with excessive holding disrupting the fight.
The officials had it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my best performance but what do champions do? They prevail," the victor stated in the ringside as he was faced disapproval from the audience.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to secure a twentieth professional win.
Several boxing experts felt Parker, 31, merited the decision but the British boxer endured the second setback of his 28-bout career.
The Champion Claims Victory in Dull Match
Buatsi's progress has stalled in recent years through promotional disputes and extended periods of lack of fights.
Once tipped as the future of British boxing, he now finds himself trying to achieve expectations - possibly in what feels like a ultimate opportunity - under fresh management.
He started carefully, with neither fighter ready to overcommit in a calculated early stages.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand in the contest, was making just his second bout at light heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a tight guard to barely take the better stanzas.
The audience's tolerance decreased amid frequent holding, with Parker going down various instances during clinches.
The underdog finished the stronger, but many rounds were challenging to assess. However, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
Buatsi advances, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Tribute Inspires Local Rivalry Fight
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a excellent all-Manchester fight to capture the European light heavyweight championship.
The venue fell silent for a deeply poignant memorial ahead of the contest as 10 bells sounded in memory of Manchester's own Ricky Hatton, who passed away 46 years old in September.
It was the premier televised fight night in the city since Hatton's death. As the concluding sound faded, the quiet transitioned to a chant of "there's just one Hatton".
The competition within the ring reflected the emotion. The eventual winner was knocked down by a significant blow flush on the jaw in the second round, standing uncertainly to his footing on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, the opponent - in rival City blue - was injured quickly, significant bruising developing under his orbital area as the fighters traded powerful shots.
The challenger, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with effective uppercuts as the intensity hardly diminished over twelve rounds.
Arthur narrowly won the result with judges scorecards of 114-114, close margin and clearer margin, but both fighters were persistent and brave, exactly what their idol the legend represented.
