UK light-heavyweight Buatsi earned a win yet unimpressive beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a split decision in a close ten-round fight at the Manchester venue.
But Parker landed significant shots, delivering effective clean blows in a match where the styles didn't complement each other, with frequent clinching marring the fight.
The scoring judges judged it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They succeed," Buatsi said in the arena as he was faced negative reactions from the spectators.
The Londoner got back to winning after his maiden career setback - an epic battle with his previous opponent in last winter - to claim a twentieth professional win.
Several boxing experts thought Parker, 31, deserved the victory but the contender suffered the second loss of his 28-bout career.
The Champion Secures Victory in Dull Affair
The fighter's advancement has plateaued in the past few years through contract problems and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what appears to be a last chance - under recent support.
He started carefully, with neither fighter ready to be aggressive in a cagey early stages.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after damaging his hand during the bout, was making just his second appearance at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who operated with a solid defense to narrowly win the better periods.
The spectators' acceptance decreased amid frequent holding, with Parker falling to the floor several times during clinches.
Parker finished the stronger, but multiple periods were difficult to score. However, ex-champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter Benavidez, and Russian champion Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Hatton Tribute Motivates All-Manchester Contest
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a excellent all-Manchester contest to capture the continental championship.
The arena became quiet for a profoundly moving homage before the fight as 10 bells sounded in honor of local hero Ricky Hatton, who passed away at age 46 in September.
It was the first major televised match card in the urban center since Hatton's death. As the last bell ended, the quiet gave way to a roar of "there's just one Hatton".
The competition during the bout reflected the emotion. Arthur was sent to the canvas by a left hook squarely on the chin in the second round, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red attire of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was damaged early, heavy swelling forming under his face as the fighters traded punishing blows.
Rea, twenty-seven, landed power punches but Arthur, 34, fought fire with fire with powerful upward punches as the pace rarely dropped over 12 rounds.
The victor edged the result with official scores of 114-114, close margin and clearer margin, but the two athletes were persistent and brave, exactly what their hero Hatton represented.
