British light-heavyweight Buatsi earned a win yet disappointing debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a split decision in a competitive ten-round fight at the Co-op Live Arena.
But Parker landed significant shots, delivering effective single shots in a fight where the techniques failed to mesh, with excessive holding spoiling the fight.
The scoring judges judged it 96-94 for to the winner, with the third a 95-95.
"It wasn't my greatest display but what do champions do? They succeed," Buatsi stated in the ring as he was met by disapproval from the spectators.
The Londoner returned to winning ways after his initial pro loss - an epic battle with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts felt the challenger, thirty-one, merited the victory but the British boxer experienced the second setback of his 28-bout professional journey.
The Champion Secures Win in Uneventful Encounter
The fighter's advancement has stalled in recent times through promotional disputes and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to fulfil that early promise - possibly in what appears to be a last chance - under new promotional backing.
He started carefully, with the two boxers ready to overcommit in a tentative early stages.
Parker, whose only previous defeat came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second fight at light-heavyweight.
By the middle rounds, Parker had stayed in contention, making life awkward for Buatsi, who utilized a tight guard to barely take the cleaner periods.
The crowd's patience diminished amid constant clinching, with the challenger going down various instances during close exchanges.
Parker closed well, but many rounds were difficult to score. Although, previous titleholder Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, giving Buatsi just a single round.
Buatsi progresses, but with the presence of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Tribute Inspires All-Manchester Contest
In the co-main event, Arthur defeated Bradley Rea by divided decision in a outstanding Manchester vs Manchester fight to secure the European light-heavyweight championship.
The arena fell silent for a deeply poignant homage ahead of the contest as a bell ceremony sounded in honor of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the first major televised boxing event in the location since Hatton's death. As the final chime disappeared, the silence gave way to a roar of "there's just one Ricky Hatton".
The fighting during the bout matched the sentiment. The eventual winner was knocked down by a significant blow flush on the chin in the early round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red equipment of Arthur soon came forward again. Across the ring, the opponent - in competitive blue - was marked up quickly, significant bruising forming under his face as the duo landed punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with powerful upward punches as the pace hardly diminished over twelve rounds.
The victor barely secured the verdict with official scores of draw, 115-113 and clearer margin, but each competitor were persistent and courageous, all the qualities their idol the legend stood for.
