UK light heavyweight Buatsi earned a win yet disappointing start to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a majority decision in a tight ten-round fight at the Co-op Live Arena.
But the challenger found success, delivering effective individual punches in a fight where the techniques didn't complement each other, with excessive holding spoiling the action.
Two judges judged it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest display but what defines champions? They win," the victor stated in the ring as he was faced negative reactions from the spectators.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to earn a 20th pro success.
Several boxing experts thought the challenger, thirty-one, deserved the decision but the Derbyshire fighter experienced the second setback of his 28-fight career.
The Champion Secures Victory in Uneventful Affair
The fighter's advancement has stalled in the past few years through management issues and extended periods of lack of fights.
Previously predicted as the next star of British boxing, he now finds himself trying to realize his potential - perhaps in what feels like a last chance - under new promotional backing.
He opened tentatively, with both competitors prepared to overcommit in a calculated opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in two years ago after damaging his hand during the bout, was competing in only his second fight at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a protective stance to narrowly win the cleaner periods.
The crowd's patience decreased amid frequent holding, with Parker going down several times during clinches.
Parker closed well, but multiple periods were difficult to score. Nevertheless, former world champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Russian star Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Tribute Fuels Local Rivalry Battle
In the co-main event, Arthur overcame Bradley Rea by close verdict in a outstanding all-Manchester fight to capture the European light heavyweight championship.
The stadium fell silent for a profoundly moving memorial prior to the bout as a bell ceremony sounded in remembrance of Manchester's own Hatton, who succumbed at age 46 in last month.
It was the first major televised match card in the city since Hatton's death. As the last bell disappeared, the quiet became a roar of "there's just one Ricky Hatton".
The competition inside the ropes equaled the sentiment. The eventual winner was knocked down by a powerful punch squarely on the face in the early round, standing uncertainly to his position on the referee's count.
But the red-colored attire of Arthur soon pressed ahead again. From the other corner, Rea - in rival City blue - was damaged quickly, noticeable damage forming under his face as the pair landed punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with stinging uppercuts as the pace rarely dropped over 12 rounds.
Arthur edged the decision with official scores of even score, narrow lead and clearer margin, but both fighters were relentless and courageous, everything their hero the legend embodied.
