British light heavyweight Buatsi made a winning yet disappointing debut to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a competitive 10-round bout at the Manchester venue.
But the challenger landed significant shots, delivering effective clean blows in a match where the approaches never quite clicked, with excessive holding marring the contest.
Two judges scored it 96-94 for to the winner, with the third a 95-95.
"It wasn't my best display but what do champions do? They succeed," Buatsi stated in the arena as he was faced boos from the audience.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in February - to claim a 20th pro success.
Some ringside observers felt Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter endured the second defeat of his 28-fight professional journey.
The Champion Secures Triumph in Uneventful Affair
The fighter's advancement has plateaued in recent years through management issues and considerable time of inactivity.
Previously predicted as the future of UK boxing, he now is positioned trying to achieve expectations - possibly in what feels like a last chance - under recent support.
He began cautiously, with both competitors ready to overcommit in a tentative opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was making just his second fight at the higher weight class.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who worked behind a solid defense to narrowly win the better periods.
The audience's tolerance diminished during regular grabbing, with Parker going down various instances during grappling.
The underdog finished the stronger, but many rounds were challenging to assess. However, former world champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the presence of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still looks steep.
Hatton Tribute Inspires Manchester Derby Battle
In the co-main event, Arthur overcame Bradley Rea by divided decision in a outstanding Manchester vs Manchester contest to win the European light heavyweight title.
The stadium grew hushed for a extremely emotional homage prior to the bout as 10 bells tolled in remembrance of local hero Hatton, who passed away 46 years old in September.
It was the premier televised match card in the city since the passing of Hatton. As the last bell faded, the stillness gave way to a roar of "there's only one Hatton".
The fighting within the ring reflected the emotion. The eventual winner was knocked down by a powerful punch squarely on the face in the early round, standing uncertainly to his footing on the referee's count.
But the Manchester United-red shorts of the fighter soon advanced again. From the other corner, the opponent - in competitive blue - was damaged soon, heavy swelling developing under his eye as the pair landed powerful shots.
The challenger, 27, landed power punches but the champion, thirty-four, matched the intensity with effective uppercuts as the pace hardly diminished over twelve rounds.
Arthur narrowly won the verdict with scoring tallies of even score, 115-113 and 115-112, but each competitor were relentless and courageous, all the qualities their inspiration the legend represented.
