British light heavyweight Buatsi secured a victory yet underwhelming debut to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a tight 10-round contest at the boxing arena.
But the challenger had his moments, landing some telling clean blows in a contest where the styles failed to mesh, with excessive holding marring the action.
Two judges scored it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my finest performance but what defines champions? They win," the victor stated in the ring as he was met by negative reactions from the crowd.
The Londoner bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to claim a 20th pro success.
Some ringside observers thought the challenger, 31, deserved the win but the British boxer endured the second defeat of his 28-bout professional journey.
Buatsi Claims Win in Slow Encounter
The fighter's advancement has plateaued in recent times through management issues and extended periods of lack of fights.
Previously predicted as the future of the British fight scene, he now finds himself trying to achieve expectations - possibly in what feels like a ultimate opportunity - under recent support.
He began cautiously, with neither fighter ready to be aggressive in a calculated opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after suffering a hand injury in the contest, was making just his second fight at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for the favorite, who operated with a tight guard to narrowly win the better periods.
The audience's tolerance diminished because of regular grabbing, with the challenger slipping to the canvas various instances during grappling.
The underdog ended stronger, but many rounds were hard to judge. Nevertheless, former world champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the likes of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Hatton Memorial Fuels Manchester Derby Battle
In the co-main event, Lyndon Arthur overcame Rea by split-decision in a terrific Manchester vs Manchester battle to win the European light-heavyweight title.
The arena became quiet for a profoundly moving homage ahead of the contest as 10 bells tolled in remembrance of local hero Hatton, who died aged 46 in September.
It was the premier televised boxing event in the city since the passing of Hatton. As the final chime ended, the stillness transitioned to a roar of "there's just one Ricky Hatton".
The competition during the bout equaled the sentiment. The eventual winner was knocked down by a significant blow flush on the jaw in the early round, getting up unsteadily to his feet on the referee's count.
But the traditional red equipment of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was injured quickly, heavy swelling developing under his face as the duo exchanged hard punches.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with stinging uppercuts as the action rarely dropped over 12 rounds.
Arthur narrowly won the result with scoring tallies of 114-114, narrow lead and clearer margin, but each competitor were persistent and brave, exactly what their hero Hatton embodied.
