UK light-heavyweight Buatsi secured a victory yet unimpressive start to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a competitive ten-round fight at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a contest where the techniques never quite clicked, with excessive holding spoiling the contest.
Two judges scored it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my best showing but what do champions do? They prevail," the victor said in the arena as he was met by boos from the spectators.
The Londoner bounced back after his maiden career setback - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Some ringside observers believed Parker, thirty-one, should have been awarded the victory but the British boxer experienced the second loss of his 28-match professional journey.
Buatsi Earns Triumph in Uneventful Affair
Buatsi's progress has plateaued in the past few years through promotional disputes and considerable time of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors willing to overcommit in a tentative early stages.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second fight at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for Buatsi, who utilized a tight guard to edge the cleaner periods.
The audience's tolerance wore thin amid constant clinching, with the challenger falling to the floor various instances during close exchanges.
The underdog closed well, but multiple periods were difficult to score. Although, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi moves on, but with the caliber of hard hitter Benavidez, and Russian champion Bivol leading the category, the path to championship success - based on this performance - still looks steep.
Hatton Tribute Inspires Manchester Derby Fight
In the supporting bout, Arthur defeated Rea by divided decision in a outstanding all-Manchester battle to win the continental belt.
The arena became quiet for a deeply poignant tribute ahead of the contest as ten bells rang in memory of the city's native Hatton, who died 46 years old in September.
It was the initial significant broadcast match card in the location since Hatton's passing. As the final chime disappeared, the stillness became a chant of "there's just one Hatton".
The action during the bout matched the emotion. Arthur was sent to the canvas by a significant blow squarely on the chin in the early round, standing uncertainly to his footing on the eight count.
But the red-colored attire of Arthur soon pressed ahead again. Across the ring, Rea - in competitive blue - was injured soon, heavy swelling developing under his eye as the fighters exchanged punishing blows.
Rea, 27, connected with strong blows but Arthur, 34, responded in kind with powerful upward punches as the action rarely dropped over 12 rounds.
Arthur edged the decision with scoring tallies of even score, close margin and wider gap, but the two athletes were persistent and brave, exactly what their idol the legend stood for.
