UK light-heavyweight Buatsi secured a victory yet underwhelming debut to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a tight ten-round bout at the Co-op Live Arena.
But the challenger found success, delivering effective single shots in a contest where the styles never quite clicked, with frequent clinching disrupting the contest.
The officials judged it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my greatest showing but what do champions do? They succeed," the victor stated in the ring as he was greeted with disapproval from the spectators.
The Londoner bounced back after his maiden career setback - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Various analysts felt Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter experienced the second defeat of his 28-fight career.
Buatsi Earns Win in Dull Encounter
Buatsi's progress has stalled in recent times through contract problems and extended periods of inactivity.
Previously predicted as the next star of British boxing, he now is positioned trying to realize his potential - maybe in what feels like a final roll of the dice - under fresh management.
He started carefully, with neither fighter willing to be aggressive in a tentative early stages.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after damaging his hand mid-fight, was making just his second fight at light-heavyweight.
By the middle rounds, Parker had kept it close, creating difficulties for Buatsi, who operated with a protective stance to edge the better stanzas.
The spectators' acceptance diminished because of regular grabbing, with the challenger slipping to the canvas multiple occasions during clinches.
Parker ended stronger, but multiple periods were difficult to score. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
The victor advances, but with the caliber of hard hitter Benavidez, and Russian star Bivol ruling the division, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Homage Inspires Manchester Derby Battle
In the co-main event, Arthur defeated Bradley Rea by split-decision in a terrific Manchester vs Manchester fight to secure the European light heavyweight championship.
The venue grew hushed for a deeply poignant memorial prior to the bout as a bell ceremony sounded in remembrance of local hero Ricky Hatton, who died 46 years old in recently.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the final chime ended, the stillness became a shout of "there's just one Ricky Hatton".
The competition inside the ropes reflected the feeling. Arthur was knocked down by a left hook flush on the jaw in the second round, rising shakily to his position on the eight count.
But the red-colored shorts of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was damaged quickly, significant bruising forming under his eye as the fighters landed punishing blows.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action seldom decreased over 12 rounds.
Arthur narrowly won the verdict with scoring tallies of 114-114, narrow lead and 115-112, but the two athletes were persistent and courageous, exactly what their hero the legend embodied.
