British light-heavyweight Buatsi made a winning yet unimpressive beginning to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a tight 10-round fight at the Manchester venue.
But the challenger had his moments, landing some telling single shots in a contest where the styles failed to mesh, with frequent clinching marring the action.
The officials had it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my finest showing but what defines champions? They succeed," the victor stated in the arena as he was faced negative reactions from the spectators.
The British fighter returned to winning ways after his first professional defeat - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers felt the challenger, 31, merited the decision but the Derbyshire fighter endured the second defeat of his 28-fight career.
Buatsi Earns Victory in Uneventful Encounter
His career development has slowed in the past few years through promotional disputes and considerable time of lack of fights.
Once tipped as the next star of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter ready to be aggressive in a cagey early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was competing in only his second bout at light heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to edge the cleaner periods.
The crowd's patience wore thin because of constant clinching, with Parker slipping to the canvas various instances during close exchanges.
Parker ended stronger, but multiple periods were hard to judge. However, ex-champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor moves on, but with the presence of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Hatton Tribute Inspires Manchester Derby Contest
In the supporting bout, Lyndon Arthur overcame Bradley Rea by close verdict in a excellent all-Manchester contest to secure the European light heavyweight title.
The arena fell silent for a profoundly moving homage before the fight as a bell ceremony rang in remembrance of the city's native Hatton, who passed away aged 46 in recently.
It was the initial significant broadcast boxing event in the urban center since Hatton's death. As the last bell disappeared, the silence transitioned to a chant of "there's only one Ricky Hatton".
The competition during the bout equaled the sentiment. The eventual winner was sent to the canvas by a powerful punch directly to the jaw in the early round, getting up unsteadily to his position on the count of eight.
But the red-colored equipment of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was damaged soon, noticeable damage forming under his face as the fighters exchanged punishing blows.
The challenger, 27, connected with strong blows but Arthur, thirty-four, responded in kind with powerful upward punches as the intensity hardly diminished over the full distance.
Arthur barely secured the decision with judges scorecards of even score, narrow lead and 115-112, but both fighters were relentless and full of heart, everything their hero the legend represented.
