British light heavyweight Buatsi earned a win yet disappointing start to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a split decision in a tight 10-round contest at the Manchester venue.
But the challenger landed significant shots, landing some telling clean blows in a contest where the techniques never quite clicked, with excessive holding disrupting the action.
Two judges had it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my greatest display but how do champions respond? They win," Buatsi stated in the ringside as he was faced disapproval from the crowd.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to earn a 20th career victory.
Various analysts felt the challenger, thirty-one, merited the decision but the British boxer endured the second loss of his 28-fight professional journey.
Buatsi Secures Win in Uneventful Match
The fighter's advancement has slowed in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the next star of UK boxing, he now stands trying to achieve expectations - maybe in what seems like a last chance - under recent support.
He opened tentatively, with both competitors willing to be aggressive in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second appearance at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for Buatsi, who worked behind a protective stance to barely take the more effective periods.
The spectators' acceptance wore thin amid frequent holding, with the challenger falling to the floor multiple occasions during grappling.
The underdog finished the stronger, but several stanzas were difficult to score. Although, previous titleholder Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor advances, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Hatton Memorial Fuels All-Manchester Fight
In the co-main event, Arthur defeated Bradley Rea by split-decision in a terrific all-Manchester contest to capture the European light-heavyweight championship.
The stadium fell silent for a deeply poignant memorial ahead of the contest as 10 bells sounded in honor of Manchester's own Ricky Hatton, who died at age 46 in September.
It was the first major televised match card in the location since Hatton's death. As the final chime ended, the quiet became a shout of "there's only one Ricky Hatton".
The action within the ring reflected the emotion. Arthur was sent to the canvas by a left hook directly to the face in the initial stage, getting up unsteadily to his footing on the referee's count.
But the traditional red shorts of Arthur soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was marked up early, noticeable damage developing under his eye as the pair exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with effective uppercuts as the action seldom decreased over 12 rounds.
Arthur narrowly won the result with scoring tallies of 114-114, close margin and wider gap, but each competitor were determined and full of heart, everything their idol the legend embodied.
