UK light-heavyweight Buatsi made a winning yet unimpressive beginning to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a close ten-round contest at the Co-op Live Arena.
But Parker found success, connecting with powerful clean blows in a fight where the approaches never quite clicked, with excessive holding spoiling the fight.
The scoring judges judged it 96-94 to the winner, with the third a 95-95.
"It wasn't my greatest display but what defines champions? They prevail," Buatsi stated in the ringside as he was met by boos from the crowd.
The Londoner got back to winning after his first professional defeat - an epic battle with Callum Smith in February - to earn a twentieth professional win.
Some ringside observers felt the challenger, 31, deserved the victory but the Derbyshire fighter suffered the second setback of his 28-match career.
The Champion Claims Win in Uneventful Match
His career development has plateaued in the past few years through contract problems and considerable time of inactivity.
Earlier forecast as the future of UK boxing, he now is positioned trying to realize his potential - perhaps in what seems like a last chance - under new promotional backing.
He opened tentatively, with both competitors willing to overcommit in a calculated initial rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after breaking his hand in the contest, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for the favorite, who utilized a protective stance to narrowly win the cleaner stanzas.
The spectators' acceptance diminished amid frequent holding, with the challenger falling to the floor multiple occasions during clinches.
Parker ended stronger, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - working with Dazn - had it particularly wide for the challenger, giving Buatsi just a single round.
The victor progresses, but with the presence of power puncher David Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Hatton Memorial Motivates Manchester Derby Fight
In the secondary fight, Arthur beat Bradley Rea by close verdict in a excellent all-Manchester battle to win the European light-heavyweight championship.
The venue fell silent for a deeply poignant memorial before the fight as a bell ceremony sounded in memory of local hero Ricky Hatton, who died aged 46 in last month.
It was the initial significant broadcast fight night in the city since Hatton's death. As the last bell faded, the silence gave way to a roar of "there's only one Hatton".
The competition within the ring matched the emotion. The eventual winner was floored by a powerful punch flush on the face in the initial stage, rising shakily to his position on the referee's count.
But the red-colored equipment of Arthur soon pressed ahead again. Across the ring, the opponent - in opposing blue - was marked up early, heavy swelling developing under his eye as the fighters landed punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the action rarely dropped over 12 rounds.
Arthur barely secured the result with official scores of draw, close margin and clearer margin, but the two athletes were relentless and full of heart, exactly what their hero the legend stood for.
