British light-heavyweight Buatsi secured a victory yet underwhelming beginning to his career under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a close ten-round fight at the Manchester venue.
But Parker landed significant shots, landing some telling single shots in a fight where the techniques never quite clicked, with excessive holding spoiling the fight.
The officials scored it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my best performance but how do champions respond? They win," Buatsi commented in the ringside as he was met by negative reactions from the audience.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Various analysts thought the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter experienced the second setback of his 28-bout professional journey.
The Champion Earns Win in Slow Encounter
His career development has slowed in recent years through management issues and long spells of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now stands trying to fulfil that early promise - maybe in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with both competitors prepared to overcommit in a tentative early stages.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after damaging his hand during the bout, was participating in his second fight at the higher weight class.
By the halfway stage, Parker had kept it close, causing problems for the favorite, who utilized a tight guard to barely take the more effective stanzas.
The crowd's patience diminished amid constant clinching, with Parker slipping to the canvas several times during grappling.
Parker ended stronger, but many rounds were difficult to score. However, former world champion Carl Frampton - commentating on Dazn - had it particularly wide for Parker, awarding Buatsi just a single round.
The victor progresses, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Hatton Tribute Motivates Manchester Derby Fight
In the co-main event, Arthur defeated Bradley Rea by split-decision in a outstanding Manchester vs Manchester contest to win the European light-heavyweight championship.
The arena grew hushed for a profoundly moving homage ahead of the contest as a bell ceremony sounded in remembrance of the city's native Hatton, who passed away aged 46 in September.
It was the first major televised fight night in the location since the passing of Hatton. As the final chime disappeared, the silence became a chant of "there's only one Hatton".
The action during the bout equaled the sentiment. Arthur was knocked down by a left hook flush on the face in the initial stage, getting up unsteadily to his position on the count of eight.
But the Manchester United-red attire of Arthur soon came forward again. On the opposite side, Rea - in competitive blue - was injured soon, noticeable damage developing under his orbital area as the duo exchanged punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the pace hardly diminished over the full distance.
Arthur barely secured the result with judges scorecards of even score, close margin and wider gap, but both fighters were relentless and courageous, exactly what their idol Hatton represented.
