British light-heavyweight Buatsi made a winning yet unimpressive beginning to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a close 10-round fight at the Co-op Live Arena.
But Parker found success, connecting with powerful individual punches in a contest where the styles didn't complement each other, with constant grabbing disrupting the fight.
The scoring judges judged it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest display but what do champions do? They prevail," the victor stated in the ringside as he was greeted with boos from the crowd.
The Londoner bounced back after his first professional defeat - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers thought Parker, thirty-one, merited the decision but the Derbyshire fighter suffered the second loss of his 28-bout professional journey.
Buatsi Claims Win in Uneventful Encounter
The fighter's advancement has plateaued in recent times through management issues and long spells of lack of fights.
Previously predicted as the next star of British boxing, he now stands trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under recent support.
He started carefully, with both competitors willing to overcommit in a cagey initial rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in 2022 after damaging his hand during the bout, was participating in his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who utilized a tight guard to edge the cleaner stanzas.
The crowd's patience wore thin because of regular grabbing, with Parker falling to the floor multiple occasions during clinches.
The underdog ended stronger, but multiple periods were difficult to score. Nevertheless, previous titleholder the boxing analyst - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Hatton Homage Inspires All-Manchester Battle
In the supporting bout, Arthur defeated Rea by split-decision in a terrific local rivalry fight to capture the continental championship.
The arena became quiet for a extremely emotional memorial prior to the bout as a bell ceremony sounded in memory of local hero Hatton, who succumbed aged 46 in recently.
It was the first major televised match card in the urban center since Hatton's passing. As the last bell ended, the stillness transitioned to a shout of "there's just one Ricky Hatton".
The competition during the bout reflected the emotion. Arthur was sent to the canvas by a left hook directly to the face in the early round, getting up unsteadily to his position on the eight count.
But the red-colored attire of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was marked up soon, noticeable damage forming under his eye as the pair exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with powerful upward punches as the pace rarely dropped over 12 rounds.
Arthur edged the decision with official scores of even score, 115-113 and clearer margin, but the two athletes were determined and courageous, everything their inspiration Hatton represented.
