UK light-heavyweight Buatsi made a winning yet underwhelming start to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a majority decision in a competitive 10-round contest at the Manchester venue.
But the challenger found success, connecting with powerful single shots in a contest where the styles never quite clicked, with excessive holding marring the contest.
The scoring judges had it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my finest showing but how do champions respond? They succeed," the victor stated in the ring as he was met by boos from the spectators.
The British fighter returned to winning ways after his first professional defeat - an epic battle with his previous opponent in February - to claim a twentieth professional win.
Some ringside observers believed the challenger, 31, deserved the decision but the contender experienced the second defeat of his 28-fight career.
The Champion Earns Win in Uneventful Encounter
Buatsi's progress has slowed in recent times through promotional disputes and extended periods of inactivity.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with neither fighter willing to overcommit in a cagey opening few rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was competing in only his second fight at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for the favorite, who worked behind a tight guard to barely take the more effective periods.
The crowd's patience decreased because of constant clinching, with Parker going down multiple occasions during clinches.
Parker finished the stronger, but several stanzas were hard to judge. Although, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, giving Buatsi just only one stanza.
Buatsi moves on, but with the likes of power puncher David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Homage Motivates Manchester Derby Fight
In the supporting bout, Arthur defeated Bradley Rea by close verdict in a terrific all-Manchester battle to capture the European light heavyweight championship.
The stadium became quiet for a profoundly moving tribute prior to the bout as a bell ceremony tolled in remembrance of Manchester's own Ricky Hatton, who died aged 46 in last month.
It was the initial significant broadcast fight night in the urban center since the passing of Hatton. As the last bell faded, the stillness gave way to a chant of "there's only one Hatton".
The competition within the ring reflected the sentiment. The eventual winner was floored by a left hook flush on the jaw in the early round, standing uncertainly to his feet on the count of eight.
But the Manchester United-red attire of Arthur soon advanced again. From the other corner, the opponent - in rival City blue - was injured early, noticeable damage developing under his eye as the pair traded punishing blows.
Rea, 27, landed power punches but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over the full distance.
Arthur narrowly won the verdict with judges scorecards of even score, 115-113 and 115-112, but both fighters were relentless and brave, everything their hero Hatton stood for.
