British light heavyweight Buatsi secured a victory yet unimpressive beginning to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a majority decision in a competitive 10-round contest at the Co-op Live Arena.
But the challenger found success, delivering effective individual punches in a fight where the approaches never quite clicked, with constant grabbing marring the contest.
The scoring judges had it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest display but what do champions do? They prevail," Buatsi stated in the ringside as he was greeted with disapproval from the crowd.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Several boxing experts felt Parker, 31, should have been awarded the decision but the Derbyshire fighter endured the second setback of his 28-match professional journey.
The Champion Secures Win in Dull Affair
His career development has slowed in the past few years through contract problems and extended periods of lack of fights.
Earlier forecast as the next star of British boxing, he now finds himself trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under recent support.
He started carefully, with both competitors prepared to be aggressive in a calculated opening few rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in 2022 after suffering a hand injury during the bout, was participating in his second fight at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who utilized a solid defense to edge the better periods.
The spectators' acceptance wore thin amid constant clinching, with the challenger going down multiple occasions during close exchanges.
The underdog finished the stronger, but multiple periods were challenging to assess. Although, ex-champion the boxing analyst - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the presence of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Hatton Memorial Motivates Local Rivalry Battle
In the supporting bout, Lyndon Arthur beat Rea by close verdict in a excellent Manchester vs Manchester fight to secure the European light-heavyweight title.
The stadium fell silent for a profoundly moving memorial prior to the bout as 10 bells tolled in memory of local hero Ricky Hatton, who died 46 years old in last month.
It was the initial significant broadcast match card in the city since Hatton's death. As the last bell disappeared, the silence transitioned to a chant of "there's just one Ricky Hatton".
The fighting during the bout matched the emotion. Arthur was sent to the canvas by a left hook flush on the jaw in the second round, getting up unsteadily to his position on the eight count.
But the Manchester United-red attire of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was injured soon, heavy swelling forming under his orbital area as the duo traded powerful shots.
Rea, 27, connected with strong blows but the champion, 34, matched the intensity with stinging uppercuts as the action seldom decreased over the full distance.
The victor narrowly won the verdict with official scores of even score, narrow lead and clearer margin, but the two athletes were determined and brave, exactly what their hero Hatton embodied.
