UK light-heavyweight Buatsi secured a victory yet unimpressive beginning to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a close ten-round bout at the Manchester venue.
But Parker found success, landing some telling individual punches in a contest where the styles didn't complement each other, with constant grabbing spoiling the action.
Two judges had it 96-94 to the winner, with the third a even score.
"It wasn't my greatest display but how do champions respond? They prevail," the victor said in the arena as he was greeted with negative reactions from the crowd.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to claim a 20th pro success.
Several boxing experts believed the challenger, thirty-one, should have been awarded the decision but the British boxer endured the second defeat of his 28-bout career.
The Champion Secures Win in Dull Affair
His career development has plateaued in the past few years through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now finds himself trying to realize his potential - possibly in what appears to be a last chance - under recent support.
He opened tentatively, with both competitors prepared to overcommit in a cagey early stages.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was making just his second appearance at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to narrowly win the cleaner stanzas.
The audience's tolerance decreased amid regular grabbing, with Parker slipping to the canvas multiple occasions during close exchanges.
The underdog finished the stronger, but many rounds were difficult to score. However, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just one round.
Buatsi progresses, but with the likes of hard hitter David Benavidez, and Russian champion Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Tribute Motivates Manchester Derby Contest
In the co-main event, Arthur defeated Bradley Rea by divided decision in a outstanding all-Manchester contest to secure the European light-heavyweight title.
The arena became quiet for a profoundly moving homage prior to the bout as ten bells sounded in memory of local hero Hatton, who died aged 46 in last month.
It was the first major televised fight night in the city since the passing of Hatton. As the concluding sound disappeared, the quiet became a chant of "there's only one Hatton".
The action during the bout equaled the feeling. The eventual winner was knocked down by a significant blow squarely on the jaw in the second round, getting up unsteadily to his feet on the count of eight.
But the red-colored shorts of Arthur soon came forward again. On the opposite side, the opponent - in opposing blue - was damaged soon, heavy swelling appearing under his face as the duo landed powerful shots.
The challenger, 27, connected with strong blows but the champion, thirty-four, matched the intensity with stinging uppercuts as the pace rarely dropped over the full distance.
The victor narrowly won the decision with official scores of draw, 115-113 and 115-112, but each competitor were persistent and courageous, all the qualities their inspiration Hatton embodied.
