British light-heavyweight Buatsi secured a victory yet disappointing debut to his career under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a split decision in a competitive 10-round fight at the boxing arena.
But the challenger had his moments, connecting with powerful single shots in a contest where the styles didn't complement each other, with frequent clinching marring the fight.
The scoring judges judged it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my best performance but what do champions do? They prevail," the victor said in the ring as he was met by disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an epic battle with his previous opponent in February - to claim a 20th pro success.
Various analysts felt Parker, thirty-one, should have been awarded the victory but the contender experienced the second loss of his 28-fight professional journey.
The Champion Secures Triumph in Slow Encounter
His career development has stalled in recent years through promotional disputes and long spells of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to realize his potential - maybe in what appears to be a final roll of the dice - under recent support.
He began cautiously, with the two boxers willing to be aggressive in a cagey opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after suffering a hand injury in the contest, was participating in his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for Buatsi, who worked behind a solid defense to narrowly win the better periods.
The spectators' acceptance decreased during regular grabbing, with Parker going down several times during close exchanges.
Parker closed well, but multiple periods were challenging to assess. However, ex-champion the boxing analyst - commentating on Dazn - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor advances, but with the caliber of heavy hitter Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Homage Inspires Local Rivalry Contest
In the secondary fight, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding Manchester vs Manchester contest to secure the continental title.
The venue fell silent for a profoundly moving homage ahead of the contest as ten bells tolled in remembrance of the city's native Hatton, who succumbed at age 46 in September.
It was the premier televised match card in the urban center since Hatton's death. As the concluding sound ended, the silence transitioned to a shout of "only one Ricky Hatton".
The fighting during the bout equaled the feeling. Arthur was sent to the canvas by a significant blow flush on the face in the second round, standing uncertainly to his position on the count of eight.
But the red-colored equipment of the fighter soon came forward again. From the other corner, Rea - in competitive blue - was damaged quickly, heavy swelling forming under his face as the pair exchanged hard punches.
Rea, 27, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the pace seldom decreased over the full distance.
The victor narrowly won the decision with scoring tallies of 114-114, close margin and clearer margin, but both fighters were persistent and courageous, all the qualities their hero Hatton stood for.
