British light-heavyweight Buatsi secured a victory yet underwhelming beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a competitive 10-round bout at the boxing arena.
But the challenger had his moments, landing some telling individual punches in a match where the techniques didn't complement each other, with constant grabbing spoiling the contest.
The scoring judges scored it 96-94 for to the winner, with the third a 95-95.
"It wasn't my best display but what do champions do? They win," the victor said in the ringside as he was met by negative reactions from the spectators.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to secure a 20th career victory.
Some ringside observers believed Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter experienced the second defeat of his 28-bout career.
Buatsi Secures Win in Slow Match
Buatsi's progress has slowed in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to realize his potential - maybe in what seems like a ultimate opportunity - under new promotional backing.
He started carefully, with neither fighter willing to overcommit in a cagey opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after damaging his hand in the contest, was participating in his second appearance at light heavyweight.
By the middle rounds, Parker had stayed in contention, making life awkward for Buatsi, who operated with a tight guard to barely take the cleaner periods.
The audience's tolerance wore thin because of constant clinching, with the challenger going down various instances during close exchanges.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
The victor advances, but with the presence of power puncher David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Hatton Tribute Fuels All-Manchester Battle
In the supporting bout, Lyndon Arthur beat Rea by split-decision in a excellent Manchester vs Manchester battle to capture the European light heavyweight championship.
The arena fell silent for a profoundly moving homage prior to the bout as a bell ceremony sounded in memory of local hero Ricky Hatton, who died at age 46 in recently.
It was the initial significant broadcast fight night in the urban center since Hatton's death. As the last bell ended, the silence transitioned to a chant of "only one Ricky Hatton".
The competition within the ring matched the sentiment. The eventual winner was knocked down by a significant blow directly to the jaw in the second round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red shorts of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was damaged quickly, heavy swelling developing under his eye as the duo exchanged hard punches.
Rea, 27, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the pace rarely dropped over twelve rounds.
Arthur barely secured the verdict with official scores of 114-114, 115-113 and clearer margin, but both fighters were relentless and brave, everything their inspiration the legend embodied.
