UK light heavyweight Buatsi secured a victory yet underwhelming beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a competitive ten-round bout at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a contest where the approaches failed to mesh, with constant grabbing marring the contest.
The officials scored it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my finest performance but how do champions respond? They succeed," the victor said in the ring as he was greeted with negative reactions from the crowd.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, merited the decision but the Derbyshire fighter experienced the second setback of his 28-match career.
Buatsi Earns Win in Slow Affair
The fighter's advancement has stalled in recent times through management issues and long spells of lack of fights.
Previously predicted as the rising talent of British boxing, he now finds himself trying to realize his potential - possibly in what feels like a last chance - under fresh management.
He opened tentatively, with both competitors ready to be aggressive in a cagey early stages.
Parker, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand mid-fight, was making just his second fight at light-heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for Buatsi, who utilized a protective stance to barely take the more effective rounds.
The crowd's patience wore thin amid frequent holding, with Parker going down multiple occasions during clinches.
The underdog ended stronger, but multiple periods were challenging to assess. Although, previous titleholder Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
The victor advances, but with the caliber of heavy hitter Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Memorial Fuels Local Rivalry Contest
In the co-main event, Arthur defeated Rea by divided decision in a outstanding local rivalry battle to win the European light heavyweight belt.
The stadium became quiet for a profoundly moving tribute ahead of the contest as a bell ceremony tolled in honor of Manchester's own Ricky Hatton, who died 46 years old in last month.
It was the first major televised boxing event in the urban center since Hatton's death. As the concluding sound faded, the silence gave way to a chant of "there's only one Ricky Hatton".
The competition inside the ropes equaled the feeling. The eventual winner was floored by a left hook directly to the jaw in the second round, rising shakily to his position on the eight count.
But the red-colored shorts of Arthur soon came forward again. From the other corner, Rea - in opposing blue - was injured early, heavy swelling forming under his face as the fighters landed punishing blows.
Rea, 27, landed power punches but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action seldom decreased over the full distance.
The victor barely secured the result with judges scorecards of draw, close margin and clearer margin, but each competitor were determined and full of heart, everything their idol the legend stood for.
