UK light-heavyweight Buatsi earned a win yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a majority decision in a tight 10-round fight at the boxing arena.
But Parker landed significant shots, delivering effective individual punches in a fight where the approaches never quite clicked, with constant grabbing spoiling the action.
The officials judged it 96-94 in favor to the winner, with the third a even score.
"It wasn't my finest display but what do champions do? They succeed," the victor said in the ringside as he was met by boos from the audience.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in February - to earn a 20th pro success.
Several boxing experts believed the challenger, 31, merited the win but the British boxer experienced the second setback of his 28-match career.
The Champion Claims Win in Slow Encounter
His career development has plateaued in the past few years through contract problems and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now finds himself trying to realize his potential - possibly in what feels like a ultimate opportunity - under recent support.
He started carefully, with neither fighter willing to overcommit in a calculated early stages.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after breaking his hand in the contest, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for the favorite, who operated with a solid defense to narrowly win the better rounds.
The spectators' acceptance decreased amid frequent holding, with the challenger slipping to the canvas several times during clinches.
Parker finished the stronger, but multiple periods were hard to judge. However, ex-champion the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
The victor advances, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Hatton Memorial Inspires Manchester Derby Fight
In the co-main event, Arthur overcame Rea by split-decision in a outstanding all-Manchester battle to capture the European light heavyweight belt.
The venue grew hushed for a profoundly moving memorial ahead of the contest as 10 bells rang in remembrance of local hero Hatton, who passed away 46 years old in recently.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the final chime disappeared, the quiet became a shout of "there's just one Ricky Hatton".
The action within the ring equaled the sentiment. Arthur was sent to the canvas by a left hook directly to the face in the early round, getting up unsteadily to his footing on the eight count.
But the red-colored shorts of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was damaged soon, heavy swelling appearing under his orbital area as the fighters traded hard punches.
Rea, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity rarely dropped over the full distance.
Arthur barely secured the decision with scoring tallies of even score, close margin and clearer margin, but the two athletes were persistent and brave, everything their inspiration the legend represented.
