British light heavyweight Buatsi made a winning yet underwhelming debut to life under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a competitive 10-round fight at the boxing arena.
But Parker had his moments, landing some telling clean blows in a match where the techniques failed to mesh, with excessive holding spoiling the fight.
The officials had it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest showing but what do champions do? They win," Buatsi commented in the ringside as he was met by negative reactions from the spectators.
The Londoner returned to winning ways after his initial pro loss - an epic battle with Callum Smith in February - to secure a 20th pro success.
Some ringside observers thought Parker, 31, deserved the victory but the contender suffered the second setback of his 28-match professional journey.
The Champion Secures Victory in Uneventful Encounter
The fighter's advancement has stalled in recent years through contract problems and considerable time of lack of fights.
Once tipped as the future of the British fight scene, he now stands trying to achieve expectations - perhaps in what feels like a ultimate opportunity - under fresh management.
He started carefully, with both competitors ready to take risks in a calculated opening few rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury in the contest, was making just his second fight at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for the favorite, who utilized a protective stance to edge the more effective periods.
The audience's tolerance diminished because of constant clinching, with the challenger going down various instances during grappling.
Parker ended stronger, but many rounds were difficult to score. Nevertheless, former world champion Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the likes of power puncher Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Tribute Motivates All-Manchester Fight
In the supporting bout, Arthur beat Rea by close verdict in a terrific Manchester vs Manchester fight to secure the European light heavyweight belt.
The venue fell silent for a profoundly moving tribute prior to the bout as ten bells rang in honor of local hero Hatton, who died 46 years old in last month.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the last bell disappeared, the silence transitioned to a chant of "there's only one Ricky Hatton".
The fighting within the ring matched the sentiment. The eventual winner was knocked down by a powerful punch flush on the jaw in the early round, rising shakily to his feet on the referee's count.
But the red-colored equipment of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was damaged early, heavy swelling forming under his face as the pair exchanged punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with effective uppercuts as the intensity rarely dropped over 12 rounds.
The victor edged the decision with official scores of even score, 115-113 and 115-112, but the two athletes were relentless and courageous, everything their idol the legend embodied.
