British light-heavyweight Buatsi earned a win yet unimpressive debut to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive 10-round fight at the boxing arena.
But Parker landed significant shots, landing some telling clean blows in a match where the styles didn't complement each other, with constant grabbing spoiling the fight.
The officials scored it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my best display but how do champions respond? They prevail," Buatsi stated in the arena as he was greeted with negative reactions from the crowd.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts believed Parker, 31, deserved the win but the contender experienced the second loss of his 28-fight career.
The Champion Secures Win in Uneventful Affair
The fighter's advancement has stalled in recent years through management issues and considerable time of inactivity.
Previously predicted as the future of the British fight scene, he now finds himself trying to realize his potential - perhaps in what seems like a last chance - under new promotional backing.
He started carefully, with neither fighter willing to take risks in a calculated early stages.
Parker, whose sole prior loss came at the lower weight class against his former opponent in 2022 after suffering a hand injury mid-fight, was competing in only his second bout at light heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for the favorite, who utilized a protective stance to edge the more effective stanzas.
The audience's tolerance decreased during regular grabbing, with the challenger going down several times during clinches.
Parker closed well, but many rounds were challenging to assess. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, giving Buatsi just only one stanza.
Buatsi progresses, but with the caliber of power puncher David Benavidez, and Russian champion Bivol ruling the division, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Memorial Motivates All-Manchester Contest
In the co-main event, Lyndon Arthur defeated Rea by split-decision in a outstanding Manchester vs Manchester fight to secure the European light heavyweight championship.
The arena grew hushed for a deeply poignant homage prior to the bout as a bell ceremony tolled in remembrance of Manchester's own Hatton, who succumbed aged 46 in last month.
It was the first major televised fight night in the urban center since the passing of Hatton. As the final chime ended, the stillness transitioned to a roar of "there's just one Hatton".
The action within the ring reflected the feeling. Arthur was knocked down by a powerful punch directly to the chin in the initial stage, rising shakily to his position on the count of eight.
But the Manchester United-red attire of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was damaged soon, noticeable damage forming under his eye as the pair exchanged hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, responded in kind with powerful upward punches as the action hardly diminished over the full distance.
Arthur barely secured the decision with scoring tallies of even score, close margin and clearer margin, but each competitor were persistent and brave, exactly what their idol the legend stood for.
