UK light heavyweight Buatsi earned a win yet underwhelming start to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a close 10-round fight at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a contest where the styles never quite clicked, with frequent clinching spoiling the fight.
The scoring judges judged it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest performance but what defines champions? They succeed," the victor stated in the ringside as he was faced negative reactions from the audience.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to secure a twentieth professional win.
Some ringside observers believed the challenger, 31, merited the victory but the Derbyshire fighter endured the second loss of his 28-fight professional journey.
Buatsi Earns Victory in Dull Encounter
The fighter's advancement has stalled in recent times through contract problems and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now is positioned trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under recent support.
He started carefully, with both competitors willing to overcommit in a cagey early stages.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was competing in only his second fight at the higher weight class.
By the halfway stage, Parker had stayed in contention, causing problems for Buatsi, who utilized a tight guard to edge the cleaner rounds.
The audience's tolerance diminished because of regular grabbing, with Parker going down various instances during grappling.
The underdog ended stronger, but several stanzas were difficult to score. Although, previous titleholder Carl Frampton - working with Dazn - had it particularly wide for Parker, giving Buatsi just a single round.
The victor progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Tribute Motivates All-Manchester Fight
In the co-main event, Arthur beat Bradley Rea by split-decision in a terrific all-Manchester contest to secure the European light-heavyweight championship.
The stadium became quiet for a extremely emotional memorial prior to the bout as a bell ceremony rang in honor of Manchester's own Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the final chime ended, the quiet became a shout of "there's only one Hatton".
The competition during the bout equaled the sentiment. The eventual winner was floored by a significant blow squarely on the face in the second round, standing uncertainly to his feet on the count of eight.
But the red-colored equipment of the fighter soon came forward again. On the opposite side, the opponent - in rival City blue - was injured quickly, noticeable damage forming under his orbital area as the pair traded punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with stinging uppercuts as the action rarely dropped over the full distance.
Arthur narrowly won the result with judges scorecards of draw, close margin and clearer margin, but the two athletes were relentless and courageous, all the qualities their hero Hatton stood for.
