UK light-heavyweight Buatsi secured a victory yet disappointing start to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a close ten-round bout at the boxing arena.
But the challenger found success, delivering effective single shots in a match where the approaches failed to mesh, with excessive holding spoiling the contest.
Two judges judged it 96-94 to the winner, with the remaining official a even score.
"It wasn't my finest display but what defines champions? They succeed," the victor commented in the arena as he was met by negative reactions from the audience.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th pro success.
Some ringside observers thought the challenger, 31, merited the victory but the Derbyshire fighter suffered the second loss of his 28-match professional journey.
The Champion Claims Victory in Dull Match
The fighter's advancement has plateaued in recent times through promotional disputes and considerable time of lack of fights.
Earlier forecast as the next star of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers ready to take risks 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 during the bout, was competing in only his second appearance at light-heavyweight.
By the middle rounds, Parker had kept it close, causing problems for Buatsi, who utilized a tight guard to edge the better stanzas.
The crowd's patience diminished during frequent holding, with the challenger going down several times during close exchanges.
The underdog finished the stronger, but multiple periods were challenging to assess. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
Buatsi moves on, but with the presence of power puncher David Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Motivates Manchester Derby Battle
In the supporting bout, Arthur overcame Bradley Rea by divided decision in a excellent all-Manchester battle to capture the continental title.
The arena became quiet for a profoundly moving memorial ahead of the contest as 10 bells sounded in remembrance of the city's native Ricky Hatton, who succumbed at age 46 in September.
It was the first major televised match card in the location since the passing of Hatton. As the last bell disappeared, the quiet became a shout of "there's only one Hatton".
The action inside the ropes matched the sentiment. Arthur was knocked down by a significant blow squarely on the chin in the early round, standing uncertainly to his position on the count of eight.
But the traditional red shorts of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was marked up soon, noticeable damage appearing under his eye as the pair exchanged hard punches.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with powerful upward punches as the pace rarely dropped over 12 rounds.
Arthur barely secured the decision with judges scorecards of draw, close margin and clearer margin, but both fighters were persistent and courageous, everything their inspiration the legend represented.
