British light heavyweight Buatsi earned a win yet unimpressive beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive ten-round contest at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful single shots in a fight where the styles failed to mesh, with frequent clinching spoiling the fight.
Two judges had it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my best display but how do champions respond? They prevail," the victor commented in the arena as he was greeted with disapproval from the spectators.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers felt Parker, 31, merited the win but the contender experienced the second defeat of his 28-match career.
The Champion Claims Triumph in Dull Match
Buatsi's progress has slowed in the past few years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the future of British boxing, he now is positioned trying to realize his potential - possibly in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with both competitors prepared to take risks in a tentative early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second bout at light heavyweight.
By the middle rounds, the underdog had kept it close, causing problems for Buatsi, who worked behind a solid defense to edge the cleaner periods.
The audience's tolerance wore thin amid frequent holding, with the challenger going down various instances during grappling.
Parker finished the stronger, but many rounds were challenging to assess. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Hatton Tribute Motivates Manchester Derby Battle
In the secondary fight, Arthur overcame Rea by close verdict in a outstanding all-Manchester battle to secure the European light heavyweight belt.
The venue fell silent for a profoundly moving tribute before the fight as a bell ceremony rang in remembrance of local hero Ricky Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the concluding sound ended, the quiet transitioned to a shout of "only one Hatton".
The fighting during the bout equaled the sentiment. Arthur was floored by a significant blow flush on the jaw in the second round, getting up unsteadily to his position on the count of eight.
But the Manchester United-red equipment of the fighter soon pressed ahead again. From the other corner, Rea - in competitive blue - was marked up early, significant bruising developing under his face as the duo exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with powerful upward punches as the pace rarely dropped over 12 rounds.
The victor edged the decision with judges scorecards of even score, close margin and 115-112, but the two athletes were relentless and courageous, exactly what their idol the legend represented.
