British light-heavyweight Buatsi made a winning yet unimpressive beginning to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a close ten-round fight at the Manchester venue.
But Parker found success, landing some telling individual punches in a match where the styles didn't complement each other, with constant grabbing spoiling the action.
The officials scored it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my best performance but what do champions do? They win," the victor commented in the ring as he was faced disapproval from the audience.
The Londoner bounced back after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, deserved the victory but the British boxer suffered the second loss of his 28-match career.
Buatsi Claims Win in Slow Match
The fighter's advancement has stalled in the past few years through contract problems and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now stands trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers ready to overcommit in a cagey early stages.
Parker, whose single earlier setback came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was competing in only his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who utilized a protective stance to edge the better rounds.
The spectators' acceptance decreased because of frequent holding, with Parker falling to the floor several times during clinches.
Parker ended stronger, but many rounds were challenging to assess. Although, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi moves on, but with the presence of power puncher David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Hatton Tribute Inspires Local Rivalry Fight
In the supporting bout, Arthur beat Bradley Rea by close verdict in a outstanding all-Manchester contest to win the continental belt.
The arena fell silent for a deeply poignant memorial ahead of the contest as ten bells sounded in remembrance of the city's native Ricky Hatton, who died 46 years old in last month.
It was the first major televised fight night in the location since the passing of Hatton. As the last bell ended, the silence gave way to a shout of "there's just one Hatton".
The fighting during the bout equaled the sentiment. The eventual winner was floored by a significant blow squarely on the face in the second round, standing uncertainly to his position on the referee's count.
But the Manchester United-red shorts of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was marked up quickly, heavy swelling developing under his eye as the duo traded powerful shots.
Rea, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with powerful upward punches as the pace rarely dropped over the full distance.
Arthur barely secured the decision with scoring tallies of even score, 115-113 and 115-112, but each competitor were persistent and courageous, all the qualities their idol the legend stood for.
