British light heavyweight Buatsi secured a victory yet unimpressive debut to life under fresh promotional backing with a unanimous decision 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 bout at the boxing arena.
But the challenger landed significant shots, landing some telling clean blows in a contest where the styles failed to mesh, with frequent clinching disrupting the fight.
The officials judged it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my finest display but how do champions respond? They succeed," Buatsi commented in the ringside as he was greeted with disapproval from the audience.
The Londoner bounced back after his maiden career setback - an epic battle with his previous opponent in February - to secure a twentieth professional win.
Various analysts felt Parker, 31, deserved the decision but the Derbyshire fighter experienced the second defeat of his 28-bout career.
Buatsi Claims Triumph in Uneventful Match
The fighter's advancement has stalled in recent times through management issues and considerable time of inactivity.
Earlier forecast as the future of UK boxing, he now stands trying to realize his potential - possibly in what seems like a final roll of the dice - under recent support.
He opened tentatively, with the two boxers ready to overcommit in a cagey opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after breaking his hand in the contest, was participating in his second fight at light heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who operated with a solid defense to edge the cleaner stanzas.
The crowd's patience diminished during constant clinching, with Parker falling to the floor various instances during grappling.
The underdog finished the stronger, but several stanzas were challenging to assess. However, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the caliber of power puncher David Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Hatton Memorial Motivates Manchester Derby Fight
In the co-main event, Lyndon Arthur overcame Bradley Rea by split-decision in a outstanding local rivalry battle to capture the continental belt.
The venue grew hushed for a deeply poignant homage ahead of the contest as ten bells tolled in remembrance of local hero Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast boxing event in the urban center since Hatton's death. As the concluding sound faded, the stillness gave way to a chant of "only one Hatton".
The action inside the ropes reflected the sentiment. Arthur was floored by a left hook directly to the jaw in the early round, rising shakily to his feet on the count of eight.
But the Manchester United-red shorts of Arthur soon came forward again. From the other corner, the opponent - in rival City blue - was marked up soon, noticeable damage developing under his eye as the fighters exchanged powerful shots.
Rea, 27, delivered effective strikes but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity rarely dropped over 12 rounds.
The victor edged the decision with scoring tallies of draw, narrow lead and 115-112, but the two athletes were relentless and brave, exactly what their idol Hatton stood for.
