UK light-heavyweight Buatsi made a winning yet unimpressive start to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a competitive 10-round bout at the boxing arena.
But the challenger landed significant shots, delivering effective single shots in a contest where the approaches didn't complement each other, with excessive holding disrupting the fight.
The officials judged it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my finest performance but what do champions do? They succeed," Buatsi stated in the ring as he was greeted with negative reactions from the crowd.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in last winter - to secure a 20th career victory.
Some ringside observers thought Parker, thirty-one, should have been awarded the decision but the contender suffered the second defeat of his 28-match professional journey.
Buatsi Claims Win in Slow Affair
His career development has plateaued in recent times through management issues and long spells of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a last chance - under fresh management.
He opened tentatively, with neither fighter prepared to be aggressive in a calculated initial rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after suffering a hand injury during the bout, was making just his second appearance at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, causing problems for the favorite, who operated with a tight guard to narrowly win the cleaner stanzas.
The audience's tolerance diminished during constant clinching, with Parker falling to the floor multiple occasions during clinches.
Parker ended stronger, but several stanzas were challenging to assess. However, ex-champion the boxing analyst - working with Dazn - had it significantly in favor for Parker, awarding Buatsi just one round.
The victor advances, but with the likes of hard hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Hatton Memorial Motivates Manchester Derby Fight
In the secondary fight, Arthur overcame Rea by close verdict in a excellent all-Manchester contest to secure the European light-heavyweight belt.
The venue became quiet for a deeply poignant memorial ahead of the contest as 10 bells sounded in honor of the city's native Ricky Hatton, who passed away aged 46 in September.
It was the first major televised match card in the location since the passing of Hatton. As the concluding sound ended, the quiet transitioned to a shout of "there's only one Ricky Hatton".
The competition during the bout matched the sentiment. The eventual winner was sent to the canvas by a significant blow flush on the chin in the initial stage, getting up unsteadily to his footing on the referee's count.
But the traditional red attire of the fighter soon came forward again. On the opposite side, the opponent - in rival City blue - was injured quickly, significant bruising developing under his face as the pair landed hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the action hardly diminished over the full distance.
The victor edged the decision with official scores of draw, narrow lead and 115-112, but each competitor were determined and courageous, exactly what their hero Hatton embodied.
