British light-heavyweight Buatsi made a winning yet underwhelming debut to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a close ten-round contest at the boxing arena.
But Parker landed significant shots, connecting with powerful individual punches in a match where the styles failed to mesh, with frequent clinching spoiling the contest.
Two judges had it 96-94 to the winner, with the third a 95-95.
"It wasn't my finest display but how do champions respond? They win," Buatsi commented in the arena as he was faced negative reactions from the audience.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to claim a 20th pro success.
Some ringside observers felt the challenger, thirty-one, merited the decision but the British boxer suffered the second loss of his 28-fight professional journey.
Buatsi Secures Win in Uneventful Match
The fighter's advancement has slowed in recent times through contract problems and long spells of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with neither fighter prepared to take risks in a tentative opening few rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after suffering a hand injury during the bout, was competing in only his second bout at light-heavyweight.
By the middle rounds, Parker had stayed in contention, making life awkward for Buatsi, who worked behind a tight guard to barely take the more effective stanzas.
The audience's tolerance decreased during regular grabbing, with the challenger slipping to the canvas various instances during grappling.
Parker closed well, but multiple periods were challenging to assess. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, giving Buatsi just a single round.
Buatsi progresses, but with the presence of hard hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Memorial Fuels All-Manchester Battle
In the co-main event, Arthur beat Bradley Rea by split-decision in a terrific Manchester vs Manchester battle to win the continental title.
The arena became quiet for a profoundly moving homage prior to the bout as ten bells sounded in honor of local hero Hatton, who succumbed 46 years old in last month.
It was the first major televised fight night in the urban center since Hatton's death. As the final chime ended, the silence transitioned to a roar of "only one Ricky Hatton".
The fighting during the bout reflected the feeling. The eventual winner was knocked down by a significant blow flush on the jaw in the second round, standing uncertainly to his feet on the eight count.
But the red-colored equipment of the fighter soon advanced again. Across the ring, the opponent - in rival City blue - was marked up soon, heavy swelling developing under his orbital area as the duo traded powerful shots.
The challenger, 27, connected with strong blows but Arthur, 34, matched the intensity with stinging uppercuts as the pace seldom decreased over 12 rounds.
Arthur edged the result with judges scorecards of even score, narrow lead and clearer margin, but both fighters were relentless and courageous, exactly what their hero the legend represented.
