UK light-heavyweight Buatsi secured a victory yet underwhelming debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a tight ten-round fight at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a contest where the techniques never quite clicked, with constant grabbing marring the fight.
Two judges scored it 96-94 to the winner, with the remaining official a even score.
"It wasn't my finest showing but what defines champions? They prevail," the victor stated in the ringside as he was met by negative reactions from the spectators.
The British fighter returned to winning ways after his initial pro loss - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts thought Parker, 31, should have been awarded the win but the Derbyshire fighter endured the second setback of his 28-fight career.
Buatsi Earns Victory in Dull Affair
His career development has slowed in the past few years through contract problems and long spells of lack of fights.
Previously predicted as the future of UK boxing, he now is positioned trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with both competitors ready to overcommit in a calculated initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was participating in his second bout at the higher weight class.
By the middle rounds, the underdog had kept it close, causing problems for the favorite, who worked behind a solid defense to edge the better periods.
The spectators' acceptance decreased because of constant clinching, with Parker going down several times during clinches.
Parker closed well, but several stanzas were difficult to score. However, previous titleholder the boxing analyst - working with the broadcast network - had it particularly wide for Parker, awarding Buatsi just a single round.
Buatsi progresses, but with the presence of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Tribute Inspires All-Manchester Fight
In the supporting bout, Arthur defeated Rea by split-decision in a outstanding local rivalry fight to capture the European light-heavyweight title.
The arena grew hushed for a deeply poignant memorial before the fight as 10 bells sounded in memory of local hero Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast fight night in the urban center since Hatton's death. As the last bell faded, the quiet transitioned to a shout of "only one Ricky Hatton".
The action within the ring matched the sentiment. The eventual winner was sent to the canvas by a left hook flush on the chin in the second round, getting up unsteadily to his footing on the count of eight.
But the traditional red equipment of the fighter soon advanced again. From the other corner, the opponent - in rival City blue - was damaged early, heavy swelling forming under his face as the fighters traded powerful shots.
Rea, 27, connected with strong blows but Arthur, 34, fought fire with fire with stinging uppercuts as the action seldom decreased over 12 rounds.
The victor narrowly won the verdict with official scores of draw, 115-113 and wider gap, but both fighters were persistent and courageous, exactly what their idol Hatton embodied.
