British light-heavyweight Buatsi secured a victory yet unimpressive debut to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a competitive ten-round fight at the Manchester venue.
But the challenger had his moments, landing some telling clean blows in a fight where the approaches failed to mesh, with frequent clinching marring the contest.
The officials scored it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my best performance but how do champions respond? They prevail," the victor stated in the arena as he was met by negative reactions from the audience.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to secure a 20th career victory.
Various analysts felt the challenger, thirty-one, should have been awarded the decision but the British boxer experienced the second setback of his 28-match career.
Buatsi Claims Win in Slow Encounter
Buatsi's progress has stalled in the past few years through management issues and considerable time of inactivity.
Once tipped as the rising talent of British boxing, he now is positioned trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with both competitors ready to be aggressive in a cagey opening few rounds.
Parker, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was competing in only his second bout at the higher weight class.
By the middle rounds, the underdog had kept it close, causing problems for the favorite, who operated with a tight guard to edge the cleaner periods.
The spectators' acceptance diminished during frequent holding, with Parker going down multiple occasions during grappling.
The underdog closed well, but many rounds were challenging to assess. Nevertheless, former world champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just a single round.
The victor advances, but with the caliber of hard hitter David Benavidez, and Russian star Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Hatton Memorial Inspires All-Manchester Fight
In the supporting bout, Arthur beat Bradley Rea by close verdict in a excellent Manchester vs Manchester battle to secure the European light heavyweight title.
The arena grew hushed for a extremely emotional tribute before the fight as ten bells tolled in remembrance of the city's native Ricky Hatton, who passed away 46 years old in recently.
It was the first major televised match card in the city since Hatton's passing. As the concluding sound faded, the silence became a shout of "only one Ricky Hatton".
The competition during the bout reflected the feeling. Arthur was knocked down by a left hook squarely on the face in the early round, standing uncertainly to his position on the eight count.
But the red-colored shorts of the fighter soon advanced again. From the other corner, Rea - in competitive blue - was damaged quickly, heavy swelling developing under his orbital area as the duo landed punishing blows.
Rea, 27, connected with strong blows but the champion, 34, responded in kind with stinging uppercuts as the pace seldom decreased over the full distance.
Arthur barely secured the result with judges scorecards of draw, narrow lead and wider gap, but each competitor were persistent and courageous, everything their hero Hatton embodied.
