British light heavyweight Buatsi earned a win yet underwhelming debut to life under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a tight 10-round bout at the boxing arena.
But the challenger had his moments, landing some telling single shots in a match where the approaches never quite clicked, with frequent clinching marring the contest.
Two judges judged it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my best showing but what do champions do? They prevail," Buatsi commented in the arena as he was faced negative reactions from the audience.
The British fighter bounced back after his maiden career setback - an memorable fight with his previous opponent in last winter - to claim a twentieth professional win.
Some ringside observers felt Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter endured the second loss of his 28-match career.
Buatsi Earns Win in Uneventful Encounter
The fighter's advancement has stalled in recent times through contract problems and long spells of lack of fights.
Earlier forecast as the next star of UK boxing, he now is positioned trying to achieve expectations - perhaps in what feels like a last chance - under fresh management.
He started carefully, with the two boxers willing to be aggressive in a cagey early stages.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after suffering a hand injury mid-fight, was participating in his second fight at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for Buatsi, who operated with a protective stance to narrowly win the better periods.
The audience's tolerance decreased amid frequent holding, with Parker falling to the floor various instances during clinches.
The underdog finished the stronger, but many rounds were difficult to score. Although, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Homage Motivates All-Manchester Fight
In the supporting bout, Arthur overcame Bradley Rea by divided decision in a excellent Manchester vs Manchester fight to capture the European light heavyweight belt.
The stadium fell silent for a deeply poignant memorial prior to the bout as 10 bells tolled in memory of the city's native Ricky Hatton, who passed away aged 46 in recently.
It was the first major televised match card in the city since the passing of Hatton. As the final chime ended, the stillness became a roar of "only one Ricky Hatton".
The competition inside the ropes equaled the emotion. Arthur was knocked down by a powerful punch flush on the chin in the initial stage, standing uncertainly to his position on the referee's count.
But the Manchester United-red shorts of Arthur soon advanced again. Across the ring, Rea - in competitive blue - was marked up early, heavy swelling developing under his face as the pair landed hard punches.
Rea, 27, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the intensity hardly diminished over twelve rounds.
Arthur narrowly won the verdict with official scores of 114-114, close margin and 115-112, but the two athletes were relentless and brave, exactly what their idol the legend embodied.
