British light-heavyweight Buatsi earned a win yet underwhelming debut to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a tight ten-round fight at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a contest where the approaches failed to mesh, with frequent clinching disrupting the action.
The scoring judges judged it 96-94 for to the winner, with the final judge a even score.
"It wasn't my finest display but what do champions do? They win," Buatsi said in the arena as he was faced negative reactions from the audience.
The Londoner got back to winning after his first professional defeat - an memorable fight with his previous opponent in last winter - to claim a 20th pro success.
Several boxing experts felt the challenger, thirty-one, should have been awarded the victory but the British boxer suffered the second setback of his 28-fight professional journey.
Buatsi Claims Victory in Slow Match
Buatsi's progress has plateaued in recent times through contract problems and long spells of lack of fights.
Previously predicted as the rising talent of the British fight scene, he now stands trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with neither fighter willing to be aggressive in a tentative 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 fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who operated with a tight guard to narrowly win the cleaner rounds.
The spectators' acceptance wore thin because of frequent holding, with Parker slipping to the canvas multiple occasions during close exchanges.
The underdog ended stronger, but several stanzas were difficult to score. However, former world champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the likes of hard hitter Benavidez, and Russian champion Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Homage Inspires Manchester Derby Contest
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a terrific all-Manchester fight to capture the European light-heavyweight championship.
The arena fell silent for a profoundly moving homage prior to the bout as 10 bells rang in honor of the city's native Ricky Hatton, who died 46 years old in last month.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the final chime disappeared, the quiet transitioned to a roar of "there's only one Hatton".
The action during the bout equaled the emotion. The eventual winner was sent to the canvas by a powerful punch directly to the face in the second round, standing uncertainly to his feet on the eight count.
But the traditional red shorts of the fighter soon pressed ahead again. Across the ring, Rea - in opposing blue - was injured soon, heavy swelling forming under his orbital area as the fighters exchanged powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with stinging uppercuts as the pace hardly diminished over twelve rounds.
Arthur narrowly won the result with official scores of draw, narrow lead and wider gap, but the two athletes were persistent and full of heart, everything their inspiration the legend stood for.
