UK light-heavyweight Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a tight ten-round bout at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a match where the techniques never quite clicked, with frequent clinching spoiling the fight.
Two judges had it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my best showing but how do champions respond? They win," Buatsi said in the ringside as he was faced disapproval from the crowd.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Several boxing experts felt the challenger, 31, deserved the decision but the British boxer suffered the second loss of his 28-bout professional journey.
Buatsi Earns Victory in Dull Encounter
The fighter's advancement has stalled in recent years through contract problems and considerable time of inactivity.
Earlier forecast as the future of British boxing, he now stands trying to realize his potential - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with both competitors willing to take risks in a cagey initial rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was participating in his second bout at light heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for Buatsi, who utilized a solid defense to edge the better rounds.
The audience's tolerance decreased during frequent holding, with the challenger falling to the floor several times during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. Although, ex-champion the boxing analyst - working with Dazn - had it particularly wide for the challenger, giving Buatsi just a single round.
The victor progresses, but with the caliber of heavy hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still looks steep.
Hatton Tribute Fuels Manchester Derby Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding all-Manchester battle to capture the European light heavyweight belt.
The arena fell silent for a profoundly moving tribute before the fight as 10 bells rang in honor of local hero Ricky Hatton, who succumbed aged 46 in recently.
It was the first major televised fight night in the location since Hatton's passing. As the final chime faded, the stillness became a chant of "there's just one Ricky Hatton".
The action during the bout matched the feeling. Arthur was sent to the canvas by a significant blow squarely on the face in the second round, getting up unsteadily to his footing on the referee's count.
But the traditional red attire of the fighter soon advanced again. On the opposite side, the opponent - in competitive blue - was injured soon, heavy swelling developing under his eye as the fighters landed hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with effective uppercuts as the action hardly diminished over twelve rounds.
Arthur narrowly won the result with scoring tallies of draw, narrow lead and 115-112, but each competitor were relentless and full of heart, all the qualities their hero Hatton stood for.
