British light heavyweight Buatsi earned a win yet unimpressive start to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a close ten-round bout at the Co-op Live Arena.
But Parker found success, landing some telling single shots in a contest where the styles didn't complement each other, with constant grabbing marring the contest.
The scoring judges had it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my greatest showing but what do champions do? They succeed," Buatsi commented in the ringside as he was greeted with negative reactions from the spectators.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to earn a 20th career victory.
Several boxing experts thought the challenger, 31, should have been awarded the victory but the British boxer suffered the second defeat of his 28-match career.
Buatsi Earns Win in Slow Encounter
His career development has stalled in recent times through management issues and considerable time of inactivity.
Earlier forecast as the future of UK boxing, he now finds himself trying to achieve expectations - possibly in what seems like a last chance - under recent support.
He opened tentatively, with neither fighter prepared to be aggressive in a tentative initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after breaking his hand mid-fight, was competing in only his second bout at the higher weight class.
By the middle rounds, Parker had made it competitive, causing problems for Buatsi, who operated with a solid defense to edge the cleaner periods.
The crowd's patience diminished amid regular grabbing, with Parker going down multiple occasions during grappling.
Parker closed well, but multiple periods were difficult to score. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi advances, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Hatton Tribute Fuels Local Rivalry Fight
In the secondary fight, Arthur beat Rea by split-decision in a excellent Manchester vs Manchester battle to win the European light heavyweight championship.
The arena grew hushed for a deeply poignant tribute prior to the bout as 10 bells tolled in honor of Manchester's own Ricky Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast match card in the location since Hatton's passing. As the final chime disappeared, the silence became a shout of "there's only one Ricky Hatton".
The action inside the ropes reflected the emotion. Arthur was floored by a left hook squarely on the jaw in the second round, rising shakily to his feet on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was injured quickly, noticeable damage forming under his eye as the pair exchanged punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with effective uppercuts as the pace rarely dropped over 12 rounds.
Arthur edged the verdict with official scores of even score, close margin and wider gap, but the two athletes were persistent and courageous, everything their inspiration the legend represented.
