UK light heavyweight Buatsi secured a victory yet disappointing start to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a competitive 10-round contest at the boxing arena.
But the challenger had his moments, delivering effective individual punches in a match where the styles never quite clicked, with frequent clinching spoiling the fight.
Two judges scored it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my finest display but what do champions do? They prevail," Buatsi said in the ringside as he was greeted with boos from the spectators.
The British fighter bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to secure a twentieth professional win.
Some ringside observers thought Parker, thirty-one, merited the victory but the contender experienced the second loss of his 28-bout career.
Buatsi Claims Win in Uneventful Match
Buatsi's progress has stalled in recent times through contract problems and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to achieve expectations - possibly in what feels like a last chance - under recent support.
He started carefully, with the two boxers prepared to overcommit in a tentative early stages.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after damaging his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the middle rounds, Parker had made it competitive, causing problems for Buatsi, who utilized a protective stance to edge the more effective periods.
The audience's tolerance diminished because of frequent holding, with the challenger falling to the floor several times during grappling.
Parker closed well, but many rounds were challenging to assess. However, former world champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
Buatsi progresses, but with the caliber of heavy hitter Benavidez, and Russian star Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Homage Motivates Local Rivalry Fight
In the co-main event, Lyndon Arthur beat Rea by divided decision in a outstanding Manchester vs Manchester battle to capture the continental title.
The stadium grew hushed for a extremely emotional memorial ahead of the contest as a bell ceremony rang in honor of local hero Ricky Hatton, who died aged 46 in September.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the last bell disappeared, the quiet gave way to a shout of "there's only one Ricky Hatton".
The competition within the ring equaled the sentiment. The eventual winner was floored by a powerful punch flush on the chin in the initial stage, standing uncertainly to his feet on the eight count.
But the Manchester United-red equipment of the fighter soon advanced again. From the other corner, Rea - in rival City blue - was marked up quickly, heavy swelling appearing under his orbital area as the duo landed powerful shots.
Rea, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with effective uppercuts as the intensity rarely dropped over 12 rounds.
Arthur barely secured the verdict with scoring tallies of even score, 115-113 and clearer margin, but the two athletes were determined and courageous, exactly what their idol the legend embodied.
