UK light-heavyweight Buatsi secured a victory yet unimpressive beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a competitive ten-round fight at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful individual punches in a match where the styles failed to mesh, with frequent clinching spoiling the contest.
The officials judged it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my best showing but what do champions do? They prevail," the victor stated in the ringside as he was greeted with negative reactions from the spectators.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Several boxing experts believed Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter endured the second setback of his 28-match career.
Buatsi Claims Triumph in Uneventful Affair
The fighter's advancement has plateaued in recent years through management issues and extended periods of lack of fights.
Once tipped as the next star of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what seems like a ultimate opportunity - under fresh management.
He started carefully, with the two boxers willing to take risks in a tentative initial rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after damaging his hand in the contest, was making just his second bout at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who operated with a protective stance to narrowly win the more effective periods.
The crowd's patience diminished because of regular grabbing, with the challenger falling to the floor several times during grappling.
Parker ended stronger, but several stanzas were challenging to assess. Although, former world champion Carl Frampton - working with the broadcast network - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor moves on, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Hatton Tribute Fuels Manchester Derby Fight
In the co-main event, Arthur defeated Bradley Rea by split-decision in a terrific all-Manchester contest to secure the European light-heavyweight belt.
The venue grew hushed for a extremely emotional homage prior to the bout as a bell ceremony rang in remembrance of the city's native Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast match card in the urban center since the passing of Hatton. As the concluding sound disappeared, the stillness transitioned to a chant of "there's only one Hatton".
The competition during the bout equaled the emotion. Arthur was sent to the canvas by a significant blow squarely on the chin in the initial stage, rising shakily to his position on the eight count.
But the red-colored attire of the fighter soon came forward again. Across the ring, the opponent - in rival City blue - was damaged early, significant bruising appearing under his face as the duo traded hard punches.
The challenger, 27, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the action seldom decreased over twelve rounds.
The victor narrowly won the decision with official scores of even score, narrow lead and clearer margin, but the two athletes were relentless and brave, all the qualities their hero Hatton stood for.
