UK light heavyweight Buatsi earned a win yet unimpressive beginning to his career under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a tight ten-round contest at the Manchester venue.
But Parker found success, landing some telling clean blows in a match where the styles never quite clicked, with constant grabbing disrupting the contest.
Two judges had it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my greatest display but what do champions do? They succeed," the victor stated in the arena as he was met by negative reactions from the spectators.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to secure a twentieth professional win.
Various analysts thought Parker, thirty-one, merited the win but the British boxer endured the second setback of his 28-bout professional journey.
The Champion Secures Triumph in Slow Encounter
The fighter's advancement has slowed in recent years through contract problems and long spells of lack of fights.
Previously predicted as the future of UK boxing, he now stands trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers prepared to overcommit 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 damaging his hand in the contest, was making just his second bout at light-heavyweight.
By the middle rounds, the underdog had kept it close, causing problems for Buatsi, who worked behind a solid defense to barely take the better rounds.
The audience's tolerance decreased amid frequent holding, with Parker slipping to the canvas multiple occasions during grappling.
The underdog ended stronger, but many rounds were difficult to score. Although, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the caliber of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Memorial Motivates All-Manchester Battle
In the secondary fight, Lyndon Arthur defeated Bradley Rea by split-decision in a excellent all-Manchester battle to win the continental belt.
The arena fell silent for a extremely emotional tribute ahead of the contest as 10 bells tolled in memory of the city's native Hatton, who died 46 years old in September.
It was the premier televised boxing event in the location since the passing of Hatton. As the final chime ended, the silence gave way to a chant of "only one Ricky Hatton".
The fighting inside the ropes reflected the sentiment. Arthur was knocked down by a left hook squarely on the jaw in the early round, rising shakily to his position on the eight count.
But the traditional red equipment of Arthur soon advanced again. From the other corner, the opponent - in rival City blue - was marked up quickly, significant bruising developing under his face as the fighters landed hard punches.
Rea, twenty-seven, landed power punches but Arthur, 34, responded in kind with effective uppercuts as the intensity hardly diminished over twelve rounds.
The victor edged the verdict with scoring tallies of 114-114, narrow lead and clearer margin, but both fighters were relentless and brave, exactly what their hero Hatton represented.
