UK light heavyweight Buatsi made a winning yet disappointing debut to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a tight 10-round bout at the boxing arena.
But Parker landed significant shots, connecting with powerful individual punches in a contest where the techniques failed to mesh, with excessive holding marring the action.
Two judges judged it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my finest display but what do champions do? They win," Buatsi stated in the arena as he was faced boos from the crowd.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to claim a 20th pro success.
Various analysts felt the challenger, thirty-one, deserved the win but the British boxer experienced the second setback of his 28-fight career.
Buatsi Earns Victory in Dull Affair
The fighter's advancement has plateaued in recent years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to achieve expectations - possibly in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter prepared to take risks in a calculated opening few rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was competing in only his second fight at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a solid defense to narrowly win the better rounds.
The audience's tolerance wore thin amid constant clinching, with Parker slipping to the canvas several times during clinches.
Parker ended stronger, but multiple periods were hard to judge. Although, previous titleholder Carl Frampton - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor progresses, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Tribute Fuels Local Rivalry Fight
In the co-main event, Arthur defeated Bradley Rea by divided decision in a outstanding local rivalry fight to capture the continental championship.
The venue became quiet for a extremely emotional homage before the fight as a bell ceremony rang in remembrance of the city's native Ricky Hatton, who passed away at age 46 in last month.
It was the first major televised boxing event in the city since Hatton's death. As the last bell ended, the stillness gave way to a shout of "there's just one Hatton".
The action inside the ropes equaled the sentiment. Arthur was floored by a significant blow squarely on the chin in the early round, rising shakily to his footing on the eight count.
But the traditional red attire of Arthur soon pressed ahead again. Across the ring, the opponent - in rival City blue - was damaged quickly, significant bruising forming under his eye as the pair landed powerful shots.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, matched the intensity with effective uppercuts as the intensity seldom decreased over 12 rounds.
The victor narrowly won the result with official scores of 114-114, 115-113 and 115-112, but the two athletes were determined and brave, exactly what their hero the legend represented.
