British light-heavyweight Buatsi secured a victory yet disappointing start to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive 10-round contest at the Manchester venue.
But the challenger found success, landing some telling single shots in a match where the styles didn't complement each other, with excessive holding spoiling the contest.
Two judges scored it 96-94 to Buatsi, with the third a even score.
"It wasn't my best display but what do champions do? They prevail," Buatsi stated in the ringside as he was faced disapproval from the crowd.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Various analysts felt the challenger, 31, deserved the decision but the contender experienced the second loss of his 28-fight career.
Buatsi Secures Victory in Slow Affair
The fighter's advancement has plateaued in recent years through management issues and extended periods of inactivity.
Previously predicted as the future of British boxing, he now is positioned trying to realize his potential - maybe in what appears to be a last chance - under fresh management.
He opened tentatively, with both competitors ready to be aggressive in a cagey initial rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was making just his second appearance at light-heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for the favorite, who worked behind a tight guard to edge the more effective rounds.
The spectators' acceptance diminished during regular grabbing, with the challenger falling to the floor various instances during grappling.
Parker finished the stronger, but multiple periods were hard to judge. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor moves on, but with the likes of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Tribute Inspires Manchester Derby Contest
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a excellent local rivalry battle to secure the European light heavyweight belt.
The stadium grew hushed for a profoundly moving tribute ahead of the contest as a bell ceremony rang in honor of the city's native Hatton, who passed away 46 years old in last month.
It was the first major televised fight night in the urban center since Hatton's death. As the final chime ended, the silence became a roar of "only one Hatton".
The competition inside the ropes matched the feeling. The eventual winner was knocked down by a significant blow flush on the jaw in the second round, getting up unsteadily to his feet on the count of eight.
But the red-colored equipment of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was injured soon, heavy swelling forming under his orbital area as the pair traded hard punches.
The challenger, 27, landed power punches but the champion, thirty-four, responded in kind with powerful upward punches as the action seldom decreased over the full distance.
The victor edged the verdict with official scores of 114-114, narrow lead and 115-112, but both fighters were relentless and full of heart, exactly what their inspiration Hatton stood for.
