UK light-heavyweight Buatsi earned a win yet unimpressive debut to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a tight 10-round fight at the Manchester venue.
But the challenger landed significant shots, connecting with powerful single shots in a match where the techniques failed to mesh, with excessive holding spoiling the contest.
The scoring judges scored it 96-94 to Buatsi, with the final judge a 95-95.
"It wasn't my finest display but what do champions do? They succeed," Buatsi said in the ringside as he was greeted with negative reactions from the audience.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in last winter - to claim a 20th pro success.
Some ringside observers felt the challenger, thirty-one, deserved the victory but the Derbyshire fighter suffered the second setback of his 28-match professional journey.
Buatsi Claims Win in Dull Match
The fighter's advancement has slowed in recent times through management issues and long spells of inactivity.
Previously predicted as the future of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what feels like a last chance - under fresh management.
He started carefully, with both competitors prepared to overcommit in a tentative early stages.
Parker, whose sole prior loss came at the lower weight class against John Ryder in 2022 after damaging his hand in the contest, was participating in his second fight at light heavyweight.
By the middle rounds, Parker had made it competitive, creating difficulties for the favorite, who utilized a solid defense to narrowly win the better stanzas.
The spectators' acceptance diminished because of constant clinching, with the challenger going down various instances during grappling.
Parker closed well, but multiple periods were challenging to assess. Nevertheless, former world champion the boxing analyst - working with the broadcast network - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Russian star Bivol ruling the division, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Tribute Fuels Manchester Derby Fight
In the secondary fight, Arthur defeated Bradley Rea by split-decision in a terrific local rivalry contest to win the continental title.
The arena became quiet for a profoundly moving homage before the fight as ten bells rang in honor of Manchester's own Ricky Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the last bell faded, the silence became a shout of "there's only one Hatton".
The action during the bout matched the emotion. Arthur was floored by a left hook directly to the face in the second round, rising shakily to his footing on the referee's count.
But the traditional red shorts of the fighter soon came forward again. From the other corner, Rea - in competitive blue - was marked up quickly, noticeable damage developing under his eye as the fighters exchanged powerful shots.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with powerful upward punches as the pace seldom decreased over the full distance.
The victor narrowly won the decision with official scores of even score, close margin and 115-112, but both fighters were persistent and full of heart, everything their idol the legend represented.
