UK light-heavyweight Buatsi made a winning yet underwhelming debut to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a tight 10-round fight at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful clean blows in a fight where the styles never quite clicked, with frequent clinching disrupting the fight.
Two judges had it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my best showing but how do champions respond? They win," the victor stated in the ring as he was met by negative reactions from the audience.
The British fighter bounced back after his maiden career setback - an thrilling contest with Callum Smith in February - to earn a twentieth professional win.
Various analysts thought the challenger, thirty-one, merited the decision but the British boxer experienced the second setback of his 28-bout career.
The Champion Claims Win in Slow Match
His career development has plateaued in recent years through management issues and extended periods of lack of fights.
Earlier forecast as the next star of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a last chance - under new promotional backing.
He began cautiously, with both competitors willing to be aggressive in a cagey initial rounds.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after breaking his hand in the contest, was making just his second appearance at light-heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for Buatsi, who operated with a tight guard to narrowly win the cleaner stanzas.
The audience's tolerance wore thin because of frequent holding, with the challenger slipping to the canvas several times during clinches.
Parker finished the stronger, but multiple periods were difficult to score. However, ex-champion the boxing analyst - working with Dazn - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor progresses, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Hatton Homage Motivates All-Manchester Fight
In the supporting bout, Arthur overcame Bradley Rea by divided decision in a terrific local rivalry battle to secure the European light-heavyweight belt.
The stadium became quiet for a extremely emotional memorial prior to the bout as ten bells sounded in memory of local hero Hatton, who died aged 46 in September.
It was the first major televised boxing event in the urban center since Hatton's passing. As the final chime ended, the stillness became a roar of "only one Hatton".
The fighting within the ring reflected the emotion. The eventual winner was sent to the canvas by a powerful punch flush on the face in the early round, getting up unsteadily to his footing on the count of eight.
But the Manchester United-red shorts of the fighter soon advanced again. On the opposite side, the opponent - in rival City blue - was marked up soon, significant bruising developing under his eye as the fighters landed powerful shots.
Rea, 27, connected with strong blows but Arthur, thirty-four, responded in kind with powerful upward punches as the action hardly diminished over the full distance.
The victor narrowly won the verdict with judges scorecards of draw, close margin and wider gap, but the two athletes were relentless and full of heart, all the qualities their inspiration the legend represented.
