British light-heavyweight Buatsi earned a win yet underwhelming beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a split decision in a competitive 10-round contest at the Manchester venue.
But the challenger had his moments, connecting with powerful individual punches in a contest where the techniques never quite clicked, with constant grabbing spoiling the fight.
The officials judged it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest showing but what defines champions? They prevail," Buatsi commented in the ringside as he was met by disapproval from the audience.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in last winter - to earn a 20th career victory.
Several boxing experts felt the challenger, thirty-one, merited the decision but the British boxer suffered the second defeat of his 28-fight career.
The Champion Secures Triumph in Uneventful Encounter
His career development has slowed in recent times through management issues and long spells of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to achieve expectations - possibly in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with both competitors ready to overcommit in a calculated early stages.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was participating in his second fight at light heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for Buatsi, who operated with a tight guard to narrowly win the better periods.
The audience's tolerance diminished during constant clinching, with the challenger going down multiple occasions during close exchanges.
Parker closed well, but multiple periods were difficult to score. However, former world champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi advances, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels Local Rivalry Contest
In the supporting bout, Arthur beat Rea by divided decision in a outstanding local rivalry fight to win the European light heavyweight title.
The venue fell silent for a profoundly moving memorial prior to the bout as ten bells tolled in remembrance of the city's native Ricky Hatton, who died aged 46 in September.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the concluding sound ended, the silence became a shout of "there's just one Ricky Hatton".
The fighting inside the ropes reflected the feeling. Arthur was knocked down by a powerful punch directly to the chin in the second round, rising shakily to his footing on the referee's count.
But the traditional red shorts of the fighter soon pressed ahead again. From the other corner, the opponent - in rival City blue - was damaged soon, significant bruising forming under his eye as the pair landed hard punches.
Rea, 27, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the action hardly diminished over 12 rounds.
Arthur edged the decision with judges scorecards of 114-114, close margin and 115-112, but each competitor were persistent and brave, all the qualities their idol Hatton represented.
