UK light-heavyweight Buatsi secured a victory yet underwhelming beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a tight ten-round bout at the boxing arena.
But the challenger landed significant shots, delivering effective clean blows in a match where the styles failed to mesh, with excessive holding disrupting the contest.
Two judges had it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my best performance but how do champions respond? They prevail," Buatsi stated in the arena as he was faced disapproval from the audience.
The British fighter returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to claim a 20th pro success.
Several boxing experts believed the challenger, thirty-one, deserved the victory but the Derbyshire fighter experienced the second defeat of his 28-match professional journey.
Buatsi Secures Win in Slow Affair
Buatsi's progress has slowed in the past few years through management issues and extended periods of lack of fights.
Once tipped as the rising talent of UK boxing, he now finds himself trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under recent support.
He started carefully, with neither fighter ready to overcommit in a cagey opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand mid-fight, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a tight guard to barely take the more effective rounds.
The audience's tolerance wore thin because of regular grabbing, with Parker slipping to the canvas various instances during close exchanges.
The underdog ended stronger, but multiple periods were challenging to assess. However, ex-champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just one round.
Buatsi progresses, but with the likes of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Ricky Hatton Memorial Inspires Local Rivalry Contest
In the supporting bout, Lyndon Arthur overcame Rea by split-decision in a excellent all-Manchester contest to win the European light-heavyweight title.
The venue grew hushed for a deeply poignant tribute prior to the bout as 10 bells rang in remembrance of the city's native Hatton, who passed away at age 46 in September.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the last bell disappeared, the silence transitioned to a shout of "there's only one Ricky Hatton".
The action within the ring reflected the feeling. The eventual winner was floored by a left hook directly to the jaw in the early round, standing uncertainly to his footing on the count of eight.
But the Manchester United-red shorts of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was damaged quickly, heavy swelling developing under his orbital area as the duo landed powerful shots.
Rea, 27, landed power punches but Arthur, 34, responded in kind with stinging uppercuts as the pace seldom decreased over 12 rounds.
Arthur edged the decision with scoring tallies of draw, 115-113 and clearer margin, but the two athletes were persistent and full of heart, everything their inspiration the legend embodied.
