UK light heavyweight Buatsi secured a victory yet unimpressive start to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a close 10-round contest at the Co-op Live Arena.
But the challenger had his moments, delivering effective single shots in a contest where the styles never quite clicked, with excessive holding marring the action.
The officials scored it 96-94 to the winner, with the remaining official a even score.
"It wasn't my best performance but how do champions respond? They prevail," the victor commented in the ring as he was greeted with negative reactions from the crowd.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to earn a 20th pro success.
Various analysts felt Parker, 31, should have been awarded the decision but the contender experienced the second setback of his 28-fight professional journey.
The Champion Earns Victory in Slow Match
Buatsi's progress has plateaued in recent times through promotional disputes and extended periods of inactivity.
Earlier forecast as the future of UK boxing, he now stands trying to realize his potential - perhaps in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with the two boxers prepared to take risks in a calculated opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after damaging his hand in the contest, was competing in only his second appearance at light heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for the favorite, who worked behind a solid defense to narrowly win the more effective rounds.
The spectators' acceptance wore thin during frequent holding, with Parker falling to the floor multiple occasions during clinches.
The underdog closed well, but several stanzas were hard to judge. Nevertheless, ex-champion Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels Local Rivalry Contest
In the co-main event, Arthur overcame Bradley Rea by close verdict in a outstanding local rivalry fight to win the European light-heavyweight title.
The venue became quiet for a deeply poignant tribute before the fight as 10 bells sounded in honor of local hero Hatton, who died at age 46 in September.
It was the first major televised match card in the urban center since the passing of Hatton. As the last bell faded, the silence became a shout of "there's only one Ricky Hatton".
The action inside the ropes matched the feeling. The eventual winner was sent to the canvas by a significant blow flush on the face in the second round, getting up unsteadily to his footing on the count of eight.
But the red-colored attire of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was marked up early, significant bruising forming under his orbital area as the fighters landed powerful shots.
Rea, 27, connected with strong blows but Arthur, 34, fought fire with fire with powerful upward punches as the intensity rarely dropped over the full distance.
Arthur edged the result with official scores of 114-114, close margin and wider gap, but both fighters were determined and full of heart, everything their hero Hatton stood for.
