British light-heavyweight Buatsi made a winning yet underwhelming debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a competitive 10-round fight at the boxing arena.
But the challenger landed significant shots, landing some telling individual punches in a contest where the techniques never quite clicked, with constant grabbing spoiling the contest.
The officials judged it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest display but what do champions do? They prevail," the victor commented in the ring as he was faced disapproval from the audience.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to secure a twentieth professional win.
Various analysts felt Parker, thirty-one, deserved the win but the British boxer endured the second setback of his 28-bout career.
The Champion Secures Win in Slow Encounter
Buatsi's progress has stalled in recent years through management issues and long spells of inactivity.
Previously predicted as the future of British boxing, he now is positioned trying to realize his potential - maybe in what feels like a final roll of the dice - under recent support.
He started carefully, with the two boxers ready to take risks in a calculated initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after breaking his hand mid-fight, was participating in his second appearance at the higher weight class.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who operated with a solid defense to barely take the more effective stanzas.
The crowd's patience diminished during regular grabbing, with the challenger falling to the floor several times during grappling.
Parker closed well, but many rounds were difficult to score. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, awarding Buatsi just a single round.
The victor progresses, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Hatton Tribute Inspires Manchester Derby Fight
In the secondary fight, Lyndon Arthur defeated Rea by divided decision in a outstanding all-Manchester battle to capture the European light heavyweight championship.
The arena grew hushed for a extremely emotional homage before the fight as ten bells rang in memory of the city's native Ricky Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the concluding sound faded, the silence transitioned to a chant of "only one Hatton".
The competition during the bout matched the feeling. Arthur was floored by a left hook flush on the jaw in the initial stage, rising shakily to his footing on the referee's count.
But the red-colored equipment of the fighter soon came forward again. From the other corner, Rea - in rival City blue - was damaged soon, significant bruising appearing under his face as the pair exchanged punishing blows.
Rea, 27, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the intensity hardly diminished over the full distance.
Arthur edged the decision with official scores of draw, 115-113 and wider gap, but each competitor were relentless and courageous, all the qualities their inspiration Hatton represented.
