UK light heavyweight Buatsi secured a victory yet underwhelming beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a tight 10-round fight at the Manchester venue.
But the challenger landed significant shots, landing some telling individual punches in a fight where the techniques failed to mesh, with excessive holding disrupting the fight.
Two judges scored it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my finest showing but how do champions respond? They prevail," the victor commented in the ring as he was met by boos from the spectators.
The British fighter got back to winning after his maiden career setback - an epic battle with his previous opponent in last winter - to secure a 20th career victory.
Various analysts felt the challenger, 31, should have been awarded the win but the Derbyshire fighter endured the second loss of his 28-bout professional journey.
The Champion Claims Win in Dull Affair
The fighter's advancement has stalled in recent years through promotional disputes and long spells of inactivity.
Once tipped as the next star of UK boxing, he now is positioned trying to realize his potential - perhaps in what feels like a final roll of the dice - under recent support.
He opened tentatively, with neither fighter ready to take risks in a cagey initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after damaging his hand mid-fight, was competing in only his second bout at light-heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who utilized a tight guard to narrowly win the cleaner periods.
The spectators' acceptance decreased during constant clinching, with the challenger going down multiple occasions during grappling.
Parker ended stronger, but many rounds were difficult to score. However, previous titleholder Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
The victor advances, but with the presence of hard hitter David Benavidez, and Russian champion Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Hatton Homage Inspires Local Rivalry Battle
In the co-main event, Arthur overcame Bradley Rea by close verdict in a terrific all-Manchester fight to secure the European light heavyweight championship.
The stadium grew hushed for a deeply poignant tribute ahead of the contest as ten bells sounded in honor of the city's native Hatton, who passed away aged 46 in September.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the concluding sound disappeared, the stillness transitioned to a roar of "there's just one Ricky Hatton".
The action within the ring matched the sentiment. The eventual winner was knocked down by a left hook squarely on the chin in the initial stage, standing uncertainly to his position on the count of eight.
But the Manchester United-red attire of Arthur soon pressed ahead again. From the other corner, the opponent - in opposing blue - was injured quickly, significant bruising developing under his orbital area as the fighters landed powerful shots.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with effective uppercuts as the intensity hardly diminished over the full distance.
Arthur barely secured the decision with official scores of draw, close margin and clearer margin, but both fighters were persistent and brave, exactly what their hero Hatton represented.
