British light heavyweight Buatsi secured a victory yet underwhelming start to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a majority decision in a competitive 10-round bout at the Manchester venue.
But Parker landed significant shots, connecting with powerful clean blows in a fight where the techniques failed to mesh, with frequent clinching spoiling the contest.
The scoring judges had it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my finest display but what do champions do? They prevail," the victor said in the ring as he was met by boos from the spectators.
The British fighter got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to claim a twentieth professional win.
Some ringside observers thought Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter suffered the second defeat of his 28-match professional journey.
The Champion Claims Triumph in Dull Encounter
The fighter's advancement has plateaued in the past few years through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to achieve expectations - possibly in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with the two boxers ready to overcommit in a cagey opening few rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand in the contest, was participating in his second fight at light heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for Buatsi, who worked behind a solid defense to edge the cleaner periods.
The spectators' acceptance diminished amid constant clinching, with the challenger going down various instances during close exchanges.
The underdog finished the stronger, but many rounds were hard to judge. However, previous titleholder the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Hatton Memorial Inspires Local Rivalry Contest
In the secondary fight, Arthur defeated Rea by close verdict in a terrific all-Manchester battle to secure the European light-heavyweight title.
The stadium fell silent for a profoundly moving tribute before the fight as 10 bells rang in remembrance of local hero Hatton, who passed away 46 years old in recently.
It was the initial significant broadcast fight night in the urban center since the passing of Hatton. As the concluding sound disappeared, the quiet became a shout of "there's only one Hatton".
The competition inside the ropes reflected the feeling. The eventual winner was sent to the canvas by a left hook directly to the chin in the early round, rising shakily to his position on the referee's count.
But the red-colored shorts of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was injured quickly, noticeable damage developing under his eye as the pair exchanged punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the intensity hardly diminished over twelve rounds.
Arthur narrowly won the result with scoring tallies of even score, close margin and clearer margin, but each competitor were relentless and courageous, everything their inspiration Hatton embodied.
