UK light heavyweight Buatsi earned a win yet disappointing debut to life under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a close ten-round fight at the boxing arena.
But the challenger landed significant shots, connecting with powerful single shots in a fight where the techniques failed to mesh, with excessive holding marring the action.
The scoring judges scored it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest showing but what defines champions? They succeed," Buatsi commented in the arena as he was greeted with boos from the spectators.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in last winter - to earn a twentieth professional win.
Several boxing experts felt the challenger, 31, merited the victory but the Derbyshire fighter suffered the second defeat of his 28-bout professional journey.
Buatsi Earns Triumph in Dull Match
Buatsi's progress has slowed in recent years through contract problems and long spells of lack of fights.
Previously predicted as the next star of UK boxing, he now finds himself trying to realize his potential - possibly in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter ready to be aggressive in a tentative opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after breaking his hand in the contest, was participating in his second appearance at light heavyweight.
By the halfway stage, Parker had made it competitive, making life awkward for Buatsi, who utilized a solid defense to barely take the more effective stanzas.
The audience's tolerance diminished amid frequent holding, with Parker slipping to the canvas various instances during grappling.
Parker finished the stronger, but many rounds were challenging to assess. Although, former world champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor advances, but with the caliber of hard hitter David Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Hatton Tribute Fuels Manchester Derby Battle
In the co-main event, Arthur beat Rea by close verdict in a outstanding Manchester vs Manchester battle to capture the European light heavyweight title.
The venue became quiet for a profoundly moving memorial before the fight as a bell ceremony rang in honor of Manchester's own Hatton, who died at age 46 in recently.
It was the first major televised boxing event in the urban center since Hatton's death. As the last bell disappeared, the quiet became a roar of "there's just one Ricky Hatton".
The action inside the ropes reflected the sentiment. The eventual winner was knocked down by a significant blow squarely on the jaw in the second round, standing uncertainly to his feet on the eight count.
But the traditional red attire of the fighter soon pressed ahead again. From the other corner, Rea - in opposing blue - was injured quickly, heavy swelling appearing under his face as the pair traded powerful shots.
The challenger, 27, landed power punches but Arthur, 34, responded in kind with effective uppercuts as the action hardly diminished over the full distance.
The victor edged the verdict with scoring tallies of 114-114, 115-113 and clearer margin, but each competitor were persistent and brave, exactly what their inspiration Hatton embodied.
