British light heavyweight Buatsi made a winning yet underwhelming beginning to his career under recent management 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 10-round bout at the boxing arena.
But Parker had his moments, connecting with powerful single shots in a contest where the approaches failed to mesh, with frequent clinching spoiling the fight.
The scoring judges judged it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my best showing but what do champions do? They prevail," Buatsi stated in the ringside as he was faced disapproval from the audience.
The Londoner got back to winning after his maiden career setback - an thrilling contest with his previous opponent in February - to secure a twentieth professional win.
Various analysts felt Parker, 31, should have been awarded the victory but the contender experienced the second defeat of his 28-match professional journey.
Buatsi Earns Win in Dull Encounter
The fighter's advancement has plateaued in recent times through contract problems and considerable time of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under recent support.
He started carefully, with neither fighter ready to take risks in a calculated opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second fight at the higher weight class.
By the halfway stage, Parker had kept it close, making life awkward for the favorite, who worked behind a protective stance to narrowly win the better rounds.
The crowd's patience diminished during regular grabbing, with the challenger slipping to the canvas multiple occasions during clinches.
The underdog closed well, but several stanzas were hard to judge. Nevertheless, former world champion Carl Frampton - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Memorial Motivates Local Rivalry Fight
In the secondary fight, Lyndon Arthur defeated Bradley Rea by divided decision in a excellent local rivalry battle to capture the continental title.
The arena became quiet for a profoundly moving homage prior to the bout as 10 bells tolled in honor of local hero Ricky Hatton, who died 46 years old in last month.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the last bell disappeared, the stillness became a roar of "there's just one Hatton".
The competition within the ring reflected the emotion. The eventual winner was knocked down by a left hook squarely on the jaw in the early round, getting up unsteadily to his position on the referee's count.
But the Manchester United-red attire of the fighter soon came forward again. Across the ring, the opponent - in opposing blue - was damaged soon, significant bruising forming under his face as the duo exchanged punishing blows.
Rea, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the intensity hardly diminished over twelve rounds.
Arthur barely secured the decision with scoring tallies of even score, 115-113 and clearer margin, but the two athletes were relentless and courageous, everything their idol the legend represented.
