British light heavyweight Buatsi secured a victory yet underwhelming debut to life under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a competitive ten-round bout at the boxing arena.
But Parker landed significant shots, connecting with powerful single shots in a match where the styles failed to mesh, with excessive holding spoiling the contest.
Two judges had it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my greatest display but what do champions do? They prevail," the victor stated in the ringside as he was met by disapproval from the spectators.
The Londoner bounced back after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a twentieth professional win.
Several boxing experts thought Parker, thirty-one, deserved the victory but the contender suffered the second setback of his 28-fight professional journey.
The Champion Earns Victory in Uneventful Match
His career development has plateaued in recent years through contract problems and considerable time of inactivity.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to achieve expectations - possibly in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors willing to be aggressive in a cagey initial rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second fight at light-heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for Buatsi, who utilized a tight guard to narrowly win the better periods.
The crowd's patience decreased amid constant clinching, with the challenger slipping to the canvas multiple occasions during grappling.
The underdog finished the stronger, but several stanzas were challenging to assess. Although, former world champion Carl Frampton - working with Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor progresses, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Hatton Homage Fuels All-Manchester Battle
In the secondary fight, Arthur defeated Bradley Rea by close verdict in a excellent local rivalry fight to win the European light heavyweight championship.
The venue became quiet for a profoundly moving homage prior to the bout as ten bells rang in memory of the city's native Ricky Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast fight night in the city since Hatton's death. As the last bell faded, the stillness transitioned to a shout of "there's just one Ricky Hatton".
The competition within the ring reflected the sentiment. The eventual winner was sent to the canvas by a left hook directly to the face in the early round, standing uncertainly to his footing on the referee's count.
But the Manchester United-red equipment of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was damaged soon, significant bruising developing under his orbital area as the fighters exchanged powerful shots.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with effective uppercuts as the pace rarely dropped over twelve rounds.
Arthur narrowly won the decision with scoring tallies of 114-114, narrow lead and clearer margin, but each competitor were determined and courageous, all the qualities their idol Hatton embodied.
