UK light heavyweight Buatsi made a winning yet unimpressive start to his career under recent management with a points victory 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 contest at the Co-op Live Arena.
But Parker landed significant shots, delivering effective individual punches in a match where the approaches never quite clicked, with constant grabbing spoiling the fight.
The scoring judges judged it 96-94 to the winner, with the final judge a even score.
"It wasn't my best showing but how do champions respond? They win," the victor commented in the ring as he was faced disapproval from the crowd.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Some ringside observers felt Parker, 31, deserved the victory but the contender endured the second setback of his 28-fight professional journey.
The Champion Secures Win in Dull Match
His career development has slowed in recent years through contract problems and considerable time of lack of fights.
Earlier forecast as the next star of British boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a last chance - under new promotional backing.
He started carefully, with neither fighter ready to be aggressive in a cagey early stages.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was making just his second bout at the higher weight class.
By the middle rounds, Parker had made it competitive, creating difficulties for Buatsi, who operated with a protective stance to narrowly win the better stanzas.
The audience's tolerance wore thin during regular grabbing, with the challenger going down several times during close exchanges.
The underdog finished the stronger, but several stanzas were difficult to score. Nevertheless, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor advances, but with the presence of heavy hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Homage Inspires Manchester Derby Fight
In the secondary fight, Arthur overcame Rea by split-decision in a excellent Manchester vs Manchester contest to secure the European light-heavyweight title.
The stadium became quiet for a extremely emotional homage ahead of the contest as a bell ceremony tolled in memory of the city's native Hatton, who died 46 years old in recently.
It was the first major televised match card in the urban center since Hatton's death. As the concluding sound faded, the quiet transitioned to a chant of "there's just one Ricky Hatton".
The action inside the ropes equaled the sentiment. The eventual winner was sent to the canvas by a left hook directly to the chin in the initial stage, standing uncertainly to his feet on the count of eight.
But the red-colored attire of Arthur soon came forward again. Across the ring, Rea - in rival City blue - was marked up soon, noticeable damage forming under his eye as the pair landed punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the pace rarely dropped over twelve rounds.
Arthur edged the verdict with official scores of 114-114, narrow lead and wider gap, but both fighters were determined and brave, all the qualities their inspiration Hatton embodied.
