UK light-heavyweight Buatsi earned a win yet underwhelming debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a judges' verdict in a competitive ten-round fight at the boxing arena.
But Parker had his moments, landing some telling single shots in a match where the styles didn't complement each other, with frequent clinching disrupting the fight.
The scoring judges scored it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my greatest display but how do champions respond? They prevail," the victor commented in the ringside as he was greeted with disapproval from the audience.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers believed Parker, thirty-one, merited the victory but the British boxer suffered the second setback of his 28-bout career.
The Champion Claims Win in Uneventful Affair
The fighter's advancement has stalled in recent times through contract problems and extended periods of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now stands trying to fulfil that early promise - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors prepared to be aggressive in a cagey early stages.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was making just his second bout at the higher weight class.
By the fight's midpoint, Parker had made it competitive, causing problems for Buatsi, who worked behind a solid defense to narrowly win the better periods.
The audience's tolerance decreased during constant clinching, with Parker going down multiple occasions during close exchanges.
Parker ended stronger, but multiple periods were difficult to score. Although, former world champion Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
The victor progresses, but with the presence of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Hatton Homage Inspires Local Rivalry Fight
In the co-main event, Arthur defeated Bradley Rea by close verdict in a terrific Manchester vs Manchester battle to secure the continental belt.
The stadium became quiet for a profoundly moving tribute ahead of the contest as a bell ceremony sounded in remembrance of Manchester's own Hatton, who succumbed at age 46 in September.
It was the premier televised boxing event in the urban center since Hatton's death. As the final chime faded, the quiet transitioned to a roar of "only one Hatton".
The competition during the bout reflected the feeling. The eventual winner was knocked down by a powerful punch flush on the face in the second round, rising shakily to his position on the referee's count.
But the traditional red equipment of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was injured early, significant bruising forming under his orbital area as the fighters exchanged powerful shots.
The challenger, 27, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the intensity seldom decreased over the full distance.
The victor barely secured the verdict with scoring tallies of draw, 115-113 and wider gap, but each competitor were determined and courageous, exactly what their hero the legend embodied.
