British light heavyweight Buatsi earned a win yet unimpressive start to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a majority decision in a tight ten-round fight at the boxing arena.
But Parker had his moments, connecting with powerful single shots in a contest where the approaches never quite clicked, with frequent clinching spoiling the contest.
The scoring judges judged it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest display but what do champions do? They prevail," the victor commented in the arena as he was faced disapproval from the audience.
The British fighter bounced back after his maiden career setback - an thrilling contest with Callum Smith in last winter - to claim a 20th pro success.
Several boxing experts believed the challenger, thirty-one, should have been awarded the win but the contender experienced the second setback of his 28-fight career.
Buatsi Earns Victory in Uneventful Match
His career development has plateaued in recent times through management issues and long spells of lack of fights.
Once tipped as the next star of UK boxing, he now stands trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under new promotional backing.
He started carefully, with neither fighter prepared to overcommit in a cagey early stages.
Parker, whose only previous defeat came at super-middleweight against his former opponent in 2022 after breaking his hand mid-fight, was participating in his second appearance at light-heavyweight.
By the middle rounds, Parker had kept it close, creating difficulties for the favorite, who operated with a solid defense to edge the better rounds.
The crowd's patience diminished during regular grabbing, with the challenger falling to the floor various instances during close exchanges.
The underdog ended stronger, but many rounds were difficult to score. Nevertheless, ex-champion the boxing analyst - working with the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - judging by this showing - still looks steep.
Hatton Homage Inspires Manchester Derby Fight
In the co-main event, Arthur overcame Rea by divided decision in a terrific local rivalry battle to secure the European light heavyweight belt.
The venue fell silent for a deeply poignant homage before the fight as ten bells tolled in honor of local hero Hatton, who passed away 46 years old in September.
It was the first major televised match card in the urban center since Hatton's passing. As the last bell disappeared, the silence gave way to a chant of "only one Ricky Hatton".
The action during the bout reflected the emotion. Arthur was sent to the canvas by a left hook flush on the face in the initial stage, rising shakily to his position on the eight count.
But the traditional red shorts of the fighter soon came forward again. On the opposite side, the opponent - in rival City blue - was damaged quickly, heavy swelling developing under his eye as the duo traded hard punches.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the action seldom decreased over 12 rounds.
Arthur edged the decision with judges scorecards of 114-114, close margin and wider gap, but each competitor were relentless and brave, everything their idol Hatton embodied.
