British light heavyweight Buatsi made a winning yet underwhelming debut to life under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a close 10-round fight at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling single shots in a contest where the techniques failed to mesh, with excessive holding disrupting the action.
The officials scored it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best display but what defines champions? They succeed," the victor commented in the arena as he was met by boos from the spectators.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in February - to claim a 20th career victory.
Various analysts felt the challenger, 31, deserved the victory but the British boxer experienced the second defeat of his 28-fight professional journey.
Buatsi Earns Triumph in Slow Encounter
Buatsi's progress has stalled in the past few years through management issues and extended periods of inactivity.
Previously predicted as the future of British boxing, he now is positioned trying to achieve expectations - possibly in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers prepared to take risks in a cagey early stages.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after breaking his hand mid-fight, was competing in only his second appearance at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for the favorite, who utilized a solid defense to narrowly win the better periods.
The crowd's patience wore thin because of constant clinching, with the challenger slipping to the canvas several times during close exchanges.
Parker closed well, but multiple periods were hard to judge. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi progresses, but with the caliber of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Homage Inspires All-Manchester Battle
In the supporting bout, Lyndon Arthur overcame Bradley Rea by split-decision in a excellent local rivalry contest to secure the continental belt.
The stadium grew hushed for a extremely emotional memorial prior to the bout as ten bells tolled in honor of Manchester's own Hatton, who passed away aged 46 in September.
It was the first major televised fight night in the urban center since Hatton's passing. As the last bell ended, the stillness gave way to a roar of "there's just one Hatton".
The action inside the ropes matched the feeling. The eventual winner was sent to the canvas by a left hook directly to the chin in the second round, rising shakily to his footing on the referee's count.
But the Manchester United-red attire of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was marked up soon, heavy swelling forming under his face as the duo landed powerful shots.
The challenger, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with powerful upward punches as the action hardly diminished over the full distance.
The victor barely secured the result with scoring tallies of even score, narrow lead and clearer margin, but the two athletes were persistent and courageous, exactly what their idol Hatton represented.
