British light-heavyweight Buatsi secured a victory yet underwhelming beginning to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a judges' verdict in a tight ten-round contest at the boxing arena.
But Parker landed significant shots, connecting with powerful individual punches in a fight where the styles failed to mesh, with constant grabbing marring the contest.
The scoring judges had it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my finest display but what defines champions? They win," the victor stated in the ringside as he was met by negative reactions from the crowd.
The Londoner bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers felt the challenger, 31, deserved the victory but the contender experienced the second defeat of his 28-match professional journey.
Buatsi Claims Win in Dull Match
Buatsi's progress has plateaued in recent times through contract problems and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now stands trying to fulfil that early promise - possibly in what seems like a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors ready to take risks in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was making just his second appearance at light heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for the favorite, who worked behind a tight guard to narrowly win the cleaner periods.
The crowd's patience wore thin amid regular grabbing, with Parker falling to the floor several times during grappling.
Parker finished the stronger, but several stanzas were hard to judge. Nevertheless, former world champion the boxing analyst - working with Dazn - had it significantly in favor for Parker, scoring for Buatsi just one round.
The victor moves on, but with the caliber of power puncher David Benavidez, and Russian star Bivol ruling the division, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels All-Manchester Battle
In the supporting bout, Arthur beat Rea by split-decision in a outstanding all-Manchester contest to win the European light heavyweight championship.
The arena fell silent for a deeply poignant homage ahead of the contest as 10 bells tolled in honor of local hero Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the last bell faded, the stillness gave way to a chant of "there's only one Ricky Hatton".
The competition during the bout reflected the feeling. The eventual winner was sent to the canvas by a significant blow flush on the chin in the early round, standing uncertainly to his footing on the referee's count.
But the red-colored shorts of Arthur soon came forward again. From the other corner, the opponent - in rival City blue - was injured early, noticeable damage forming under his eye as the duo landed hard punches.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over 12 rounds.
Arthur barely secured the decision with judges scorecards of 114-114, narrow lead and 115-112, but the two athletes were persistent and full of heart, all the qualities their hero the legend stood for.
