UK light heavyweight Buatsi earned a win yet disappointing start to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a competitive ten-round contest at the Co-op Live Arena.
But Parker landed significant shots, delivering effective individual punches in a match where the techniques didn't complement each other, with constant grabbing marring the fight.
The officials judged it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my best display but what defines champions? They succeed," the victor stated in the arena as he was faced boos from the spectators.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to earn a twentieth professional win.
Some ringside observers felt Parker, thirty-one, deserved the win but the British boxer experienced the second defeat of his 28-bout professional journey.
Buatsi Earns Triumph in Dull Match
Buatsi's progress has plateaued in recent times through contract problems and considerable time of inactivity.
Earlier forecast as the future of British boxing, he now stands trying to achieve expectations - perhaps in what feels like a last chance - under new promotional backing.
He opened tentatively, with the two boxers willing to be aggressive in a cagey opening few rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was making just his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who operated with a protective stance to edge the better stanzas.
The crowd's patience diminished during regular grabbing, with the challenger slipping to the canvas multiple occasions during grappling.
Parker ended stronger, but several stanzas were challenging to assess. Although, former world champion the boxing analyst - working with Dazn - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the presence of heavy hitter David Benavidez, and Russian champion Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Hatton Tribute Motivates All-Manchester Contest
In the co-main event, Arthur overcame Bradley Rea by close verdict in a excellent all-Manchester battle to capture the European light heavyweight championship.
The venue became quiet for a deeply poignant tribute prior to the bout as 10 bells sounded in memory of local hero Ricky Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast match card in the urban center since the passing of Hatton. As the last bell disappeared, the quiet became a chant of "only one Hatton".
The competition within the ring matched the feeling. The eventual winner was knocked down by a powerful punch squarely on the face in the early round, getting up unsteadily to his position on the referee's count.
But the Manchester United-red attire of the fighter soon advanced again. On the opposite side, the opponent - in competitive blue - was damaged early, noticeable damage appearing under his face as the pair exchanged punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with effective uppercuts as the action rarely dropped over twelve rounds.
Arthur barely secured the verdict with official scores of 114-114, close margin and wider gap, but the two athletes were determined and full of heart, exactly what their hero the legend stood for.
