UK light-heavyweight Buatsi earned a win yet unimpressive beginning to life under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a tight ten-round fight at the boxing arena.
But the challenger found success, delivering effective individual punches in a fight where the approaches never quite clicked, with constant grabbing disrupting the contest.
The scoring judges had it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best showing but how do champions respond? They win," the victor commented in the arena as he was faced negative reactions from the spectators.
The British fighter bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts felt Parker, thirty-one, merited the victory but the British boxer suffered the second defeat of his 28-match professional journey.
Buatsi Earns Win in Slow Match
The fighter's advancement has stalled in the past few years through management issues and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to realize his potential - possibly in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with neither fighter willing to be aggressive in a calculated initial rounds.
Parker, whose only previous defeat came at super middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second bout at light-heavyweight.
By the middle rounds, Parker had made it competitive, causing problems for Buatsi, who utilized a protective stance to barely take the more effective periods.
The crowd's patience decreased during frequent holding, with Parker falling to the floor several times during close exchanges.
Parker closed well, but several stanzas were challenging to assess. Although, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for Parker, awarding Buatsi just a single round.
The victor advances, but with the caliber of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Tribute Motivates Manchester Derby Fight
In the supporting bout, Arthur overcame Rea by split-decision in a outstanding Manchester vs Manchester fight to secure the European light heavyweight title.
The venue fell silent for a profoundly moving memorial ahead of the contest as 10 bells rang in memory of Manchester's own Ricky Hatton, who passed away 46 years old in last month.
It was the premier televised match card in the location since Hatton's passing. As the concluding sound ended, the quiet transitioned to a shout of "only one Ricky Hatton".
The competition inside the ropes equaled the feeling. Arthur was sent to the canvas by a significant blow squarely on the jaw in the early round, getting up unsteadily to his feet on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. Across the ring, Rea - in rival City blue - was injured soon, significant bruising developing under his eye as the fighters exchanged powerful shots.
Rea, twenty-seven, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the intensity hardly diminished over twelve rounds.
The victor barely secured the result with judges scorecards of 114-114, narrow lead and 115-112, but both fighters were relentless and full of heart, exactly what their inspiration Hatton represented.
