British light-heavyweight Buatsi secured a victory yet underwhelming beginning to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close 10-round fight at the Manchester venue.
But Parker landed significant shots, connecting with powerful single shots in a fight where the techniques failed to mesh, with frequent clinching disrupting the contest.
The scoring judges scored it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my best showing but how do champions respond? They win," Buatsi commented in the ringside as he was met by negative reactions from the crowd.
The Londoner returned to winning ways after his initial pro loss - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers believed Parker, thirty-one, deserved the decision but the Derbyshire fighter experienced the second defeat of his 28-match professional journey.
Buatsi Earns Victory in Dull Match
Buatsi's progress has plateaued in recent times through promotional disputes and extended periods of inactivity.
Earlier forecast as the future of the British fight scene, he now stands trying to achieve expectations - maybe in what appears to be a last chance - under new promotional backing.
He began cautiously, with both competitors willing to take risks in a calculated early stages.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after damaging his hand mid-fight, was participating in his second fight at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, causing problems for the favorite, who operated with a solid defense to narrowly win the better stanzas.
The spectators' acceptance decreased because of frequent holding, with Parker falling to the floor multiple occasions during clinches.
Parker closed well, but multiple periods were difficult to score. However, former world champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor advances, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still looks steep.
Hatton Tribute Fuels Local Rivalry Contest
In the co-main event, Arthur defeated Rea by split-decision in a terrific Manchester vs Manchester contest to win the continental title.
The venue became quiet for a deeply poignant memorial prior to the bout as a bell ceremony tolled in memory of local hero Ricky Hatton, who died at age 46 in September.
It was the initial significant broadcast match card in the city since Hatton's passing. As the concluding sound faded, the quiet gave way to a shout of "there's just one Hatton".
The competition during the bout equaled the feeling. Arthur was sent to the canvas by a significant blow directly to the jaw in the second round, getting up unsteadily to his position on the eight count.
But the red-colored equipment of Arthur soon came forward again. From the other corner, Rea - in opposing blue - was marked up early, heavy swelling forming under his orbital area as the pair exchanged hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the pace rarely dropped over twelve rounds.
The victor barely secured the result with official scores of 114-114, 115-113 and 115-112, but the two athletes were relentless and courageous, all the qualities their hero the legend represented.
