UK light-heavyweight Buatsi secured a victory yet disappointing beginning to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a majority decision in a competitive 10-round fight at the Manchester venue.
But the challenger found success, delivering effective clean blows in a contest where the styles never quite clicked, with frequent clinching spoiling the action.
Two judges had it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my finest display but how do champions respond? They win," Buatsi said in the arena as he was met by boos from the spectators.
The British fighter bounced back after his initial pro loss - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Various analysts felt Parker, 31, merited the victory but the Derbyshire fighter suffered the second loss of his 28-match career.
Buatsi Secures Victory in Uneventful Affair
Buatsi's progress has slowed in recent times through contract problems and long spells of inactivity.
Once tipped as the next star of the British fight scene, he now is positioned trying to achieve expectations - possibly in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors ready to be aggressive in a calculated initial rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was competing in only his second bout at light heavyweight.
By the halfway stage, the underdog had kept it close, creating difficulties for Buatsi, who operated with a tight guard to edge the more effective stanzas.
The audience's tolerance diminished during frequent holding, with the challenger slipping to the canvas multiple occasions during close exchanges.
The underdog ended stronger, but several stanzas were difficult to score. Although, former world champion the boxing analyst - working with the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the journey to titles - on this evidence - still appears challenging.
Hatton Tribute Motivates Manchester Derby Battle
In the supporting bout, Lyndon Arthur beat Rea by divided decision in a outstanding all-Manchester battle to win the European light-heavyweight championship.
The stadium grew hushed for a extremely emotional tribute ahead of the contest as 10 bells sounded in remembrance of the city's native Ricky Hatton, who died at age 46 in last month.
It was the initial significant broadcast fight night in the location since Hatton's death. As the final chime disappeared, the quiet transitioned to a shout of "there's just one Hatton".
The action during the bout reflected the feeling. The eventual winner was floored by a significant blow directly to the jaw in the second round, standing uncertainly to his position on the referee's count.
But the Manchester United-red attire of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was marked up quickly, noticeable damage developing under his face as the fighters landed hard punches.
The challenger, 27, landed power punches but Arthur, 34, matched the intensity with effective uppercuts as the intensity seldom decreased over twelve rounds.
Arthur barely secured the result with official scores of 114-114, 115-113 and wider gap, but each competitor were persistent and courageous, everything their inspiration Hatton represented.
