British light-heavyweight Buatsi secured a victory yet underwhelming start to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a split decision in a close 10-round fight at the Co-op Live Arena.
But the challenger found success, landing some telling clean blows in a contest where the techniques failed to mesh, with excessive holding spoiling the contest.
Two judges judged it 96-94 to the winner, with the final judge a even score.
"It wasn't my best performance but what do champions do? They win," the victor said in the arena as he was met by negative reactions from the crowd.
The British fighter bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to claim a 20th pro success.
Some ringside observers believed Parker, thirty-one, deserved the win but the British boxer experienced the second loss of his 28-fight professional journey.
Buatsi Earns Victory in Dull Match
His career development has slowed in recent times through contract problems and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to realize his potential - maybe in what seems like a last chance - under recent support.
He started carefully, with the two boxers willing to take risks in a calculated early stages.
Parker, whose single earlier setback came at the lower weight class against his former opponent in 2022 after damaging his hand mid-fight, was competing in only his second appearance at the higher weight class.
By the middle rounds, the underdog had stayed in contention, causing problems for Buatsi, who utilized a tight guard to edge the cleaner stanzas.
The audience's tolerance wore thin because of regular grabbing, with the challenger slipping to the canvas multiple occasions during clinches.
The underdog finished the stronger, but many rounds were difficult to score. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi 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 seems difficult.
Ricky Hatton Tribute Inspires Local Rivalry Contest
In the co-main event, Arthur beat Bradley Rea by split-decision in a terrific Manchester vs Manchester contest to win the European light-heavyweight belt.
The stadium fell silent for a extremely emotional tribute before the fight as ten bells tolled in memory of the city's native Ricky Hatton, who died aged 46 in last month.
It was the initial significant broadcast fight night in the city since Hatton's death. As the final chime faded, the stillness gave way to a shout of "only one Ricky Hatton".
The action within the ring matched the sentiment. The eventual winner was knocked down by a left hook flush on the jaw in the early round, getting up unsteadily to his feet on the count of eight.
But the traditional red shorts of the fighter soon advanced again. Across the ring, Rea - in opposing blue - was damaged soon, heavy swelling developing under his face as the duo exchanged hard punches.
The challenger, 27, delivered effective strikes but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity rarely dropped over twelve rounds.
The victor barely secured the result with official scores of draw, close margin and clearer margin, but the two athletes were determined and full of heart, everything their idol the legend represented.
