British light heavyweight Buatsi earned a win yet unimpressive start to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a close ten-round bout at the Co-op Live Arena.
But the challenger found success, delivering effective individual punches in a contest where the styles never quite clicked, with excessive holding marring the contest.
The officials had it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my best showing but what defines champions? They succeed," the victor stated in the ring as he was faced boos from the spectators.
The British fighter bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts felt the challenger, thirty-one, merited the decision but the British boxer experienced the second defeat of his 28-match career.
The Champion Secures Win in Slow Affair
The fighter's advancement has slowed in recent times through contract problems and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to realize his potential - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers prepared to be aggressive in a cagey early stages.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand mid-fight, was making just his second appearance at the higher weight class.
By the fight's midpoint, Parker had made it competitive, creating difficulties for the favorite, who utilized a solid defense to narrowly win the better rounds.
The crowd's patience decreased during frequent holding, with the challenger slipping to the canvas several times during clinches.
Parker ended stronger, but several stanzas were difficult to score. Although, previous titleholder the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi progresses, but with the caliber of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Tribute Fuels All-Manchester Battle
In the co-main event, Arthur overcame Rea by close verdict in a excellent local rivalry contest to win the continental championship.
The arena fell silent for a profoundly moving memorial prior to the bout as a bell ceremony tolled in honor of the city's native Hatton, who died 46 years old in recently.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the last bell ended, the stillness became a shout of "there's just one Hatton".
The competition inside the ropes equaled the emotion. The eventual winner was sent to the canvas by a left hook directly to the chin in the early round, rising shakily to his footing on the count of eight.
But the Manchester United-red attire of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was damaged soon, heavy swelling developing under his face as the pair landed hard punches.
Rea, 27, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the action seldom decreased over twelve rounds.
Arthur barely secured the decision with scoring tallies of even score, 115-113 and wider gap, but both fighters were determined and full of heart, all the qualities their inspiration the legend represented.
