UK light heavyweight Buatsi made a winning yet underwhelming debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a tight ten-round bout at the boxing arena.
But the challenger landed significant shots, landing some telling individual punches in a match where the techniques failed to mesh, with frequent clinching disrupting the contest.
The scoring judges judged it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my greatest performance but how do champions respond? They succeed," Buatsi said in the ringside as he was met by disapproval from the spectators.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers felt the challenger, 31, merited the win but the contender suffered the second loss of his 28-match career.
The Champion Secures Win in Slow Encounter
The fighter's advancement has stalled in recent times through promotional disputes and long spells of inactivity.
Previously predicted as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - maybe in what feels like a last chance - under fresh management.
He opened tentatively, with both competitors ready to take risks in a tentative opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was making just his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for the favorite, who operated with a tight guard to edge the more effective rounds.
The audience's tolerance diminished during regular grabbing, with the challenger slipping to the canvas several times during grappling.
Parker closed well, but several stanzas were difficult to score. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, awarding Buatsi just a single round.
Buatsi moves on, but with the caliber of heavy hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - judging by this showing - still appears challenging.
Hatton Memorial Inspires All-Manchester Fight
In the secondary fight, Lyndon Arthur overcame Rea by close verdict in a terrific all-Manchester fight to win the European light-heavyweight championship.
The arena fell silent for a extremely emotional homage ahead of the contest as a bell ceremony tolled in remembrance of Manchester's own Hatton, who succumbed aged 46 in last month.
It was the first major televised match card in the city since the passing of Hatton. As the last bell disappeared, the stillness gave way to a roar of "there's only one Ricky Hatton".
The action during the bout reflected the sentiment. Arthur was floored by a left hook squarely on the jaw in the second round, rising shakily to his position on the referee's count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was injured early, significant bruising forming under his orbital area as the duo traded hard punches.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity rarely dropped over the full distance.
The victor edged the decision with judges scorecards of 114-114, 115-113 and wider gap, but the two athletes were determined and courageous, all the qualities their inspiration the legend embodied.
