UK light-heavyweight Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a close ten-round fight at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a fight where the techniques didn't complement each other, with frequent clinching marring the action.
The scoring judges had it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my finest showing but how do champions respond? They succeed," Buatsi commented in the ring as he was met by disapproval from the audience.
The British fighter bounced back after his first professional defeat - an memorable fight with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers thought the challenger, 31, merited the victory but the British boxer endured the second loss of his 28-match career.
Buatsi Earns Victory in Uneventful Affair
The fighter's advancement has slowed in recent years through promotional disputes and considerable time of lack of fights.
Earlier forecast as the future of UK boxing, he now is positioned trying to realize his potential - perhaps in what appears to be a final roll of the dice - under fresh management.
He started carefully, with the two boxers willing to take risks in a tentative early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was making just his second fight at light-heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for the favorite, who utilized a solid defense to narrowly win the cleaner stanzas.
The crowd's patience wore thin amid frequent holding, with Parker falling to the floor various instances during grappling.
Parker finished the stronger, but several stanzas were difficult to score. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it particularly wide for the challenger, giving Buatsi just a single round.
Buatsi moves on, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Hatton Memorial Fuels Manchester Derby Fight
In the co-main event, Lyndon Arthur beat Rea by close verdict in a excellent Manchester vs Manchester contest to secure the European light-heavyweight belt.
The stadium grew hushed for a extremely emotional homage ahead of the contest as ten bells sounded in honor of Manchester's own Ricky Hatton, who died aged 46 in recently.
It was the premier televised match card in the urban center since the passing of Hatton. As the final chime faded, the quiet became a shout of "there's just one Ricky Hatton".
The competition within the ring reflected the emotion. The eventual winner was knocked down by a significant blow squarely on the chin in the early round, getting up unsteadily to his footing on the eight count.
But the Manchester United-red attire of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was injured early, noticeable damage forming under his face as the fighters exchanged punishing blows.
Rea, 27, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the intensity hardly diminished over twelve rounds.
Arthur barely secured the result with official scores of even score, close margin and clearer margin, but the two athletes were persistent and full of heart, all the qualities their inspiration the legend embodied.
