UK light heavyweight Buatsi secured a victory yet underwhelming start to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a close 10-round contest at the boxing arena.
But the challenger had his moments, landing some telling single shots in a contest where the approaches never quite clicked, with frequent clinching spoiling the action.
The scoring judges had it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my best display but what do champions do? They succeed," the victor commented in the ring as he was met by boos from the spectators.
The British fighter returned to winning ways after his initial pro loss - an epic battle with Callum Smith in February - to earn a 20th pro success.
Some ringside observers felt the challenger, thirty-one, merited the win but the British boxer endured the second defeat of his 28-match professional journey.
The Champion Claims Win in Slow Match
Buatsi's progress has plateaued in the past few years through promotional disputes and considerable time of lack of fights.
Previously predicted as the next star of British boxing, he now finds himself trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter ready to overcommit in a calculated early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second fight at light heavyweight.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who worked behind a protective stance to narrowly win the more effective rounds.
The audience's tolerance diminished amid constant clinching, with the challenger falling to the floor various instances during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor advances, but with the likes of heavy hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Memorial Inspires Manchester Derby Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by divided decision in a outstanding local rivalry contest to secure the European light-heavyweight belt.
The venue became quiet for a profoundly moving memorial ahead of the contest as ten bells sounded in memory of local hero Ricky Hatton, who died 46 years old in September.
It was the premier televised fight night in the urban center since Hatton's passing. As the concluding sound disappeared, the stillness became a shout of "there's just one Hatton".
The action inside the ropes reflected the feeling. The eventual winner was knocked down by a significant blow flush on the face in the second round, getting up unsteadily to his position on the referee's count.
But the red-colored attire of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was injured soon, significant bruising forming under his face as the pair exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the action seldom decreased over the full distance.
Arthur edged the verdict with judges scorecards of draw, narrow lead and clearer margin, but the two athletes were determined and brave, exactly what their idol the legend embodied.
