British light-heavyweight Buatsi made a winning yet underwhelming debut to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a close 10-round contest at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling individual punches in a contest where the approaches didn't complement each other, with constant grabbing disrupting the contest.
Two judges judged it 96-94 to the winner, with the remaining official a even score.
"It wasn't my finest display but what do champions do? They win," Buatsi stated in the arena as he was met by disapproval from the spectators.
The Londoner bounced back after his maiden career setback - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Various analysts believed the challenger, 31, merited the victory but the British boxer experienced the second setback of his 28-match professional journey.
Buatsi Earns Triumph in Dull Affair
His career development has stalled in recent years through contract problems and considerable time of lack of fights.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with neither fighter prepared to overcommit in a cagey opening few rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was participating in his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for the favorite, who worked behind a solid defense to barely take the better periods.
The audience's tolerance wore thin amid frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
Parker closed well, but several stanzas were challenging to assess. Nevertheless, ex-champion the boxing analyst - commentating on Dazn - had it significantly in favor for Parker, scoring for Buatsi just one round.
The victor moves on, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Homage Inspires All-Manchester Contest
In the co-main event, Lyndon Arthur beat Bradley Rea by close verdict in a excellent Manchester vs Manchester contest to win the European light heavyweight title.
The arena became quiet for a profoundly moving homage before the fight as a bell ceremony sounded in honor of Manchester's own Hatton, who died aged 46 in last month.
It was the premier televised match card in the urban center since the passing of Hatton. As the final chime ended, the stillness gave way to a shout of "there's only one Hatton".
The fighting inside the ropes reflected the sentiment. Arthur was floored by a powerful punch directly to the chin in the second round, getting up unsteadily to his feet on the count of eight.
But the red-colored shorts of Arthur soon pressed ahead again. Across the ring, the opponent - in opposing blue - was injured soon, significant bruising forming under his orbital area as the fighters landed punishing blows.
The challenger, twenty-seven, landed power punches but the champion, 34, fought fire with fire with powerful upward punches as the action seldom decreased over twelve rounds.
The victor barely secured the verdict with judges scorecards of 114-114, close margin and wider gap, but the two athletes were persistent and courageous, all the qualities their hero Hatton embodied.
